Conceit means one sees and admires himself and his actions. It is a psychological condition which we sometimes find in ourselves. The meanings given to it, that have been mentioned in language books, mostly explain its requirements or consequences such as elation, arrogance, and denying what others hold against you as objectionable, according to Al-Munjid.
These meanings, as you can see, are among the requirements of the state which we mentioned in one's nafs. As regarding the idiomatic meaning for conceit, according to the definition of the scholars of mannerism, it is, according to some scholars of the hereafter, magnifying the blessing, taking it for granted while forgetting to attribute it to the One Who bestowed it.
`Allama al-Majlisi, may Allāh sanctify his soul, has said that conceit is magnifying the good deed, seeing it as plentiful. As regarding feeling pleased with it while feeling humble to the most Exalted One and thanking Him for enabling its doing, it is good, commendable.
I say that what this great traditionist has said, that is, conceited is "one who sees himself as not having fallen short of undertaking the deed", a reference to a particular conduct to which narrations have referred. Among such traditions is one recorded in the sacred book Al-Kāfi from the father of al-Hassan, namely Imām Mousa son of Ja'fer, peace be with both of them, who said once to one of his sons, "O son! You have to maintain your endeavor.
Do not ever think of yourself as having transcended the stage of falling short of perfecting your worship of Allāh, the most Exalted, the most Great, and are obeying Him, for Allāh is never adored as He should be." It is also as the Messenger of Allāh (ص) had said, being the best of all descendants of Adam, the one who is the best of them in his knowledge of Allāh, and the one who adored Him the best, addressing Him thus: "We did not know You as You ought to be known, nor did we adore You as You should rightly be adored." Al-Kāfi, too, cites Jābir [son of Abdullāh al-Ansāri] saying that the father of Imām Ja'fer (ع) said to him, "O Jābir! May Allāh never get you out of the feeling of being neglectful and of being derelict in worshipping Allāh."
The great traditionist, 'allama al-Majlisi, has quoted the knowledgeable critic, the great scholar, and the most revered mentor Bahā ad-Deen al-`Āmili, may Allāh be pleased with him, saying, "There is no doubt that if one does a righteous deed, such as fasting on certain days, spending the night praying and the like, feels happy about it. If he feels like that on account of these deeds being a boon from Allāh, a blessing from Him, the most Exalted One, upon him, while being afraid of their disappearance, pleading to Allāh to grant him more of them…, such feeling is not conceit. But if he thinks that they represent his own characteristic, that they are done by his person, being attributed to him, thinking much of them and feeling reliant upon them, seeing himself as being outside the limit of dereliction, having the attitude as if he is doing Allāh, Praise to Him, a favor because of them, such is conceit."