The reasons behind my enlightenment are many, but I shall only mention a few of them here:
1. The text regarding the succession to the Caliphate
I have committed myself, before embarking on this study, to never depending on any reference unless it is considered authentic by the two parties, and to discarding those references that are solely referred to by only one of the parties.
Thus, I shall investigate the idea regarding the preference between Abu Bakr and Ali ibn Abi Talib, and that the succession of the caliphate was by written text [Dictate] for Ali, as the Shiites claim, and not by election and Shura [consultation] as the Sunnis claim.
Any researcher in this subject, if he considers nothing but the truth, will find that the text in support of Ali is very clear, like the following saying by the Messenger of Allah: Whoever considers me his master, then Ali is his master. He said it at the end of the Farewell Pilgrimage, when it was confirmed that Ali would succeed, and many people congratulated him on that, including Abu Bakr and Umar who were among the well-wishers, and who were quoted as having said to the Imam, Well done, Ibn Abi Talib, overnight you have become a master of all the believers." 
If the reader wants more information, he may read "al- Ghadir" by al-Amini (thirteen Volumes) in which the writer classifies the sayings of the Prophet according to the Sunnis.
As for the alleged popular election of Abu Bakr on "The Day of al-Saqifah" and his subsequent acclamation in the mosque; it seems that it was just an allegation without foundation. How could it be by popular agreement when so many people were absent during the acclamation? People like: Ali, al-Abbas, most of the house of Bani Hashim, Usama ibn Zayd, al-Zubayr, Salman al-Farisi, Abu Dharr al-Ghifari, al-Miqdad ibn al-Aswad, Ammar ibn Yasir, Hudhayfa ibn al-Yaman, Khuzayma ibn Thabit, Abu Burayd al-Aslami, al-Bura ibn Azib, Abu Ka'b, Sahl ibn Hanif, Saad ibn Ubada, Qays ibn Saad, Abu Ayyub al-Ansari, Jabir ibn Saad, Khalid ibn Saad, and many others. 
The acclamation of Abu Bakr was without consultation, in fact it took the people by surprise, especially when the men in charge of the Muslim affairs were busy preparing for the funeral of the Messenger of Allah. The citizens of al-Medinah were shocked by the death of their Prophet, and then they forced the acclamation  on the people. and even threatened to burn the house of Fatima if those who were absent from the acclamation refused to leave it. So how could we say that the acclamation was implemented through consultation and popular agreement?
The answer, is that there is no evidence or proof with the Sunnis and al-Jamaah.
Therefore, what the Shiites say regarding this issue is right, because it has been established that the Sunnis have the text which proves the succession of Ali to the caliphate, but they deliberately misinterpret it to maintain the Companion's honour. Thus, the just and fair person has no choice but to accept the text, especially if he knows the circumstances that surrounded the case. 
The subject is agreed upon by the two parties, and the fair and sensible person has no choice but to judge Abu Bakr as being wrong, that is if he did not admit his injustice and bad treatment of the leading lady.
Anyone who cares to follow the events of that tragedy and studies its various facts will recognize that Abu Bakr deliberately hurt al-Zahra and denied her argument so that she could not protest against him - supported by the texts of al-Ghadir and others - regarding the lawful right for her husband and cousin to the succession of the caliphate. There are many indications that have been mentioned by historians which lead us to believe in accounts of these events, this is one of them:
Al-Zahra - may Allah's peace be upon her - went around the meeting places of al-Ansar, asking for support for her cousin and husband and they said, "O daughter of the Messenger of Allah, we have already acclaimed that man, and if your husband and cousin had approached us before him, we would have supported him." Ali - may Allah honour his face - said, "Would I leave the Messenger of Allah (saw) in his house unburied and go to argue with people about his authority?" Fatimah said, "Abu al-Hasan did what was expected from him, and for what they did Allah will hold them responsible and accountable." 
Firstly, the grave of al-Zahra is unknown and nobody knows exactly where it is; some say it is in the Prophet's chamber, others say it is in her house opposite the Prophet's chamber, and there are people who think that it might be in al-Baqi', in the midst of Ahl al-Bayt's graves.
This is the first fact that I deduced: al-Zahra (as) wanted the Muslims, through generations to come, to know why she asked her husband to bury her secretly during the night, and that not one of them attend her funeral ! Thus, every Muslim could reach certain interesting facts when researching into historical events.
Secondly, I discovered that the visitor who wants to visit Uthman ibn Affan's grave has to go a long way until he reaches the end of al-Baqi', and there he finds it by a wall. By contrast, he will find the burial places of most of the Companions at the beginning of al-Baqi', near the entry. Even Malik ibn Anas, the famous jurist, who was a follower of the Followers, is buried near the burial places of the Messenger's wives. It became clear to me what the historians meant when they said that he was buried in "Hash Kawkab". which was Jewish land, because the Muslims refused to bury him in the Baqi' of the Messenger of Allah. When Muawiya seized power, he bought that land from the Jews and included it in al-Baqi', so that it contains the grave of his cousin Uthman. He who visits al-Baqi' today will see this fact very clearly.
It is astonishing to know that Fatimah al-Zahra (as) was the first of the Prophet's children to die after him, and at the most there were six months between the departure of the father and his daughter, and despite that, she was not buried beside her father.
Fatimah al-Zahra, as I mentioned earlier, stated in her will that she should be buried secretly, therefore, she was not buried beside her father. But what about her son, al-Hasan, why was he not buried beside his grandfather? Aisha (Umm al-Mumineen) prevented that. When al-Husayn brought his brother to bury him by his grandfather, the Messenger of Allah, Aisha rode a mule and went around saying, "Do not bury someone I do not love in my house." Then, the houses of Bani Umayya and Hashim stood opposite each other ready to fight, but al-Husayn told her that he would only take the coffin of his brother around the grave of their grandfather then he would bury him in al-Baqi'. That was because Imam al-Hasan requested from his brother, that no blood should be shed for his sake. Ibn Abbas said a few verses regarding this event:
"She rode a camel , she rode a mule , if she had lived longer, she would have ridden an elephant, you have the ninth of the eighth, and you took everything."
It is worth mentioning here a story related to the subject of inheritance that has been cited by many historians:
Ibn Abi al-Hadid al-Mutazili said in his commentary on Nahj al-Balagha: Aisha and Hafsa came to see Uthman, during his caliphate, and asked him to give them their shares of what they had inherited from the Messenger of Allah (saw). Uthman was stretched on the sofa, so he sat up and said to Aisha: You and that woman sitting next to you brought a man who cleansed himself with his urine and testified that the Messenger of Allah (saw) said, "We, the prophets, do not leave an inheritance." If the Prophet truly did not leave any inheritance, why do you ask for it now, and if he left an inheritance, why did you deprive Fatimah of her legal share? After that, she left him feeling very angry and said: Kill Na'thal, for he has become an unbeliever. 
One of the reasons which led to my enlightenment and ultimately made me leave the tradition [Sunna] of my forefathers was the comparison between the positions of Ali ibn Abi Talib and that of Abu Bakr, based on logical deductions and historical references.
As I started in earlier parts of this book, I only included in my research the references which have been agreed on by both, the Shiites and the Sunnis.
I searched in the books of both parties and found that only Ali received total support, and both Shiites and Sunnis agreed on his leadership in accordance with the texts they approved of. However there is neither support nor agreement on the leadership of Abu Bakr except by a small group of Muslims, and we have mentioned what Umar said about his succession to the caliphate. Furthermore. there are many virtues and good deeds attributed to Ali ibn Abi Talib by the Shiites and cited as authentic references in the Sunni books. The sayings are full of the virtues of Ali, more than any other Companion ever received, and even Ahmed ibn Hanbal said: No one among the Companions of the Messenger of Allah (saw) had more virtues than Ali ibn Abi Talib. 
Regarding that Imam al-Shafi'i says: I am surprised about a man whose virtues were kept secret by his enemies, out of envy, and were kept secret by his followers, out of fear, but nevertheless, an enormous amount of them spread."
As for Abu Bakr, I searched in the books of the two parties, and found that the virtues attributed to him by the Sunnis were much less than that attributed to Ali. The virtues of Abu Bakr that have been mentioned in historical books were narrated either by his daughter Aisha, whose position vis-a-vis Ali is well documented, and she tried hard to support her father, even by fabricating sayings, or by Abdullah ibn Umar, who was never close to Ali, and he was one of those who refused to pay homage to Ali despite the popular support he had received. Abdullah ibn Umar used to say that the best people after the Prophet were Abu Bakr then Uthman, and after that everybody was equal . Thus, he made Imam Ali like any other ordinary person, without preferences or virtues.
The virtues of Abu Bakr were also mentioned by Amr ibn al-'As, Abu Hurayrah, Urwa and Ikrima, and all of them hated Ali and fought him either with arms or by plotting against him and attributing virtues to his enemies.
Ahmed ibn Hanbal said, "Ali had many enemies who searched hard to find a fault attributable to him, but they could not, so they brought a man whom Ali had-fought and battled with, and praised him because of their hatred towards Ali." . But Allah said: "Surely they will make a scheme, and I too will make a scheme so glad the unbelievers a respite: let them alone for a while" [Holy Qur'an 86:15-17].
What Banu Harb have done to them is nothing in comparison to what you did to them,
How many times have you clearly violated the Religion?
And how much of the Prophet's [family's] blood Has been spilt by you?
You pretend to be his followers, but on your hands Is the blood of his purified sons.
After having finished with all these sayings, and having came out from the darkness, I leave the last judgement to Allah, and there will be no more excuses from the people after all that.
Despite the fact that Abu Bakr was the first caliph, and had all the power and authority, despite the bribes and gifts that the Umayyads gave to every one who praised Abu Bakr, Umar and Uthman, and despite all the alleged virtues and good deeds that they invented for Abu Bakr, which filled many books ... despite all that, they did not amount to a fraction of the true virtues of Imam Ali.
Furthermore, if we analyze the alleged sayings that were in favour of Abu Bakr, we find them incompatible with the historical facts, and no sensible man or creed could accept them. Earlier on we explained the saying attributed to the Prophet: "If the faith of Abu Bakr and the faith of my nation is put on the balance, the faith of Abu Bakr will be heavier".
If the Messenger of Allah was aware of this high degree of faith in Abu Bakr, he would not have appointed Usama to command the army; nor would he have refused to bear witness for him as he did for the martyrs of Uhud, and then said to him that he did not know what he was going to do after him", so that Abu Bakr  cried. In addition to that, the Prophet would not have sent Ali ibn Abi Talib to take "Surat Bara'a" from him and prevented him from transmitting it. 
Thus, we find total agreement from both parties regarding Ali alone, also historical facts point out that the correct acclamation was for Ali alone.
He abstained, but the Muhajireen and Ansar insisted on his acclamation; then when he was finally nominated, some people refused to pay homage to him, but he never forced them to change their minds.
On the other hand we find that the acclamation of Abu Bakr was a "mistake" - as Umar ibn al-Khattab put it - "may Allah protect the Muslims from its evil." The acclamation of Umar was based on a promise given to him by Abu Bakr. The acclamation of Uthman was a historical comedy: Umar nominated six people for the caliphate and told them to choose one candidate, and said if four agreed and two disagreed, then the two should be killed, however, if the six were divided into two equal camps, then the camp which was supported by Abdul Rahman ibn Awf should be considered. but if after a certain time passed and no agreement had been reached, the whole six should be killed. The story is long and rather strange, but the important thing is that Abdul Rahman ibn Awf chose Ali on the condition that he should rule in accordance with the Book of Allah [the Qur'an] and the tradition of His Messenger and the tradition of the two Shaykhs: Abu Bakr and Umar. Ali refused these conditions but Uthman accepted them, so he became caliph. Ali came out from the conference of the acclamation and knew in advance the result, and talked about it in his famous speech known as al-Shaqshaqiyya.
After Ali, Muawiya took over the caliphate and changed it to a hereditary system within Bani Umayya, and after them came Bani al- Abbas where the caliphs succeeded one after the other either by personal nomination [from the previous caliph] or by means of force and seizure of power. From the beginning of the Islamic era until Kamal Ataturk - who abolished the Islamic caliphate - there has been no correct acclamation  except that for the Commander of the Believers Ali ibn Abi Talib.
The prophetic traditions which persuaded me to follow Imam Ali were those I have read in the Sihahs of the Sunnis and were approved by the Shiites, and they have many more. But as usual I only referred to the prophetic traditions that have been agreed on by both parties, and here are some of them:
A. The Prophetic tradition: "I am the city of Knowledge and Ali is its gate."
This tradition  alone should be sufficient to indicate the example that has to he followed after the Messenger of Allah (saw) because the educated man ought to be followed.
Say: "Are those who know and those who do not know alike?"
[Holy Quran 39:9]
He also said:
"Is He then Who guides to the truth more worthy to be followed, or he who himself does not go aright unless he is guided? What then is the matter with you; how do you judge?" [Holy Quran 10:35]
History has recorded many facts telling us that Ali was the most knowledgeable man among all the Companions and they used to consult him on every important matter, and we do not know of any event in which he declined to give his advice.
Abu Bakr said, "May Allah never put me in a predicament that Abu al-Hasan cannot solve. " And Umar said, "If it was not for Ali, Umar would have perished." 
And this is what Imam Ali said about himself, "Ask me before you lose me. By Allah, if you ask me about anything that could happen up to the Day of Judgement, I will tell you about it. Ask me about the Book of Allah, because by Allah there is no [Qur'anic] verse that I do not know whether it was revealed during the night or the day, or whether it was revealed on a plain or on a mountain." 
"And fruits and herbage, A provision for you and for your cattle" [Holy Quran 80:31-32]
Abu Bakr replied, "Which sky would give me shade, and which land would carry me if I say something I do not know about the Book of Allah." And this is Umar saying. "All people are more knowledgeable than I am, even women." He was once asked about the meaning of a Qur'anic verse, and his reaction was to rebuke the man and beat him until he bled, then he said, "Do not ask about matters which may appear bad to you." 
In his "commentary", al-Tabari stated that Umar once said the following, "My knowledge of al-Kalalah is more valuable to me than owning a palace similar to those in Syria."
In one of his books, Ibn Maja quoted Umar as saying "There are three things, if they were explained by the Messenger of Allah, I would have loved them more dearly than anything in the world: Al-Kalalah, usury and the caliphate." God forbid that the Messenger of Allah stayed silent on these subjects!
B. The Prophetic tradition: O Ali! You hold in relation to me the same position as Haroon held in relation to Moses, except that there shall be no prophet after me.
This tradition, as should be apparent to every sensible person, shows the special quality of the Commander of the Believers, Ali, which made him the right person to be the supporter, the guardian and the deputy [or successor] of the Messenger of Allah as Haroon was the supporter, guardian and deputy of Moses when he went to meet his God. There is also the position of Ali vis-a-vis the Prophet which is absolutely equal to the relation between Haroon and Moses, except for the prophethood, which was excluded in the same tradition.
Furthermore, we find in the tradition the fact that Imam Ali was the best Companion, who only came second after the Messenger of Allah (saw).
C. The Prophetic tradition: Ali is the master of all those of whom I am master. O Allah! Love him who loves him and hate him who hates him, help him who helps him, forsake him who forsakes him, and turn justice with him wherever he turns.
This tradition alone is sufficient to reply to the allegations concerning the seniority of Abu Bakr, Umar and Uthman to Ali, who was appointed by the Messenger of Allah as the guardian after him of all the faithful. It is of no consequence for whoever tried to interpret the saying as the friend or the support in order to divert it from its original meaning so that the integrity of the Companions may be kept intact. The Messenger of Allah stood up in the terrible heat addressing the people, saying, "Do you witness that I have a prior right to and superior authority over all the faithful?" They replied, "Yes, O Messenger of Allah. " Thereupon he said, "Ali is the master of all those whom I am a master. . . etc." This is a clear text indicating that the Messenger of Allah had appointed Ali as his successor to lead the nation [of Islam], and the fair and sensible person could not but accept this interpretation and refuse that of the others, thus preserving the integrity of the Messenger of Allah before preserving the integrity of the Companions. Those who give an alternative interpretation to the saying are in fact ridiculing the wisdom of the Messenger of Allah, who gathered the multitude of people, in that unbearable heat, to tell them that Ali was the friend and supporter of the faithful. And what do those, who misinterpret the text in order to preserve the integrity of their masters, say about the procession of congratulation that the Messenger of Allah organised for Ali? It started with the wives of the Messenger, the mothers of the faithful, then Abu Bakr and Umar came and said to him, "Well done Ibn Abi Talib, Overnight you became the guardian [master] of all the faithful."
In fact all the historical evidence gives clear indications that those who misinterpret the above tradition are liars. Woe to those who wrote what they wrote, and woe to them for what they are writing. Allah - the Most High - said. "...a party of them most surely conceal the truth while they know it" [Holy Qur'an 2:146].
D. The Prophetic tradition: Ali is from me and I am from Ali and no one can discharge my duty except myself or Ali.
This honourable tradition  is another clear indication that Imam Ali was only one whom the Messenger authorized to discharge his duties. The Messenger said it on the day of the great pilgrimage when he sent Ali with Surat Bara'a instead of Abu Bakr, who came crying and asked, "O Messenger of Allah ! Reveal something for me." The Messenger answered, "My Lord ordered me that nobody can discharge my duty except myself or Ali."
The Prophet of Allah (saw) said, indicating Ali. This is my brother, my trustee and my deputy [caliph] after me, so listen to him and obey him." 
Also, in al-Tabari's commentary [Tafsir], Volume 19. Page 121, when the Prophet says "My trustee and my deputy [caliph]" was changed to "This is my brother etc. etc", but they failed to recognize that al-Tabari had cited the tradition in its entirety in his Annals Volume 2, Page 319. Look how they change the words and distort the facts ... they want to put out the light of Allah with their mouths, but Allah is spreading His light.
During my investigation I wanted to see the truth, so I searched for the first edition of "The Life of Muhammad". and after some hard work - praise be to Allah - found it, although it cost me considerably. The important thing is that I looked at the distortion and became convinced that the evil people are trying the best they can do to remove the facts. because there is strong evidence in the hands of their "enemies".
When the fair investigator comes across such a blatant distortion, he will no doubt begin to keep away from them and become convinced that they have no evidence except lies and distorted facts. They hire writers to whom they give money, titles and false university degrees in order to write for them books and articles through which they insult the Shiites and accuse them of blasphemy, while at the same time they defend the position, even if it is unjust, of some of the Companions who turned on their heels and exchanged right for wrong after the departure of the Messenger of Allah.
Allah says: "Even thus said those before them, the like of what they say; their hearts are all alike. Indeed We have made the verses clear for a people who are sure." [Holy Quran 2:118]