Thank you for your question. Both well being and difficulty are types of ordeal that a person is tested with, in the same way that wealth and poverty are both tests but in different ways. While difficulties require patience, well being requires thankfulness (which means not only being thankful with the tongue but using their opportunities to fulfill the goals Gid has set out for a human). Those that do fulfill this responsibility will be rightly rewarded in the next life, in the same way that those who are patient through their trials will be rewarded.
The difference in trial is decided by God, who will only put a believer in the best situation for their progression. Fairness here is not that everyone has the same trial, but that everyone is given the best opportunity according to their constitution. A person tested with difficulty may succeed where they would have failed with ease, and vice verca. However, what is more usual in life is that people are tested with a variety of circumstances some of which are difficult and some of which are easy. A person that has no difficulty in life whatsoever is perhaps one who is lead astray, as another function of well being is to distract those with a bad end.
For a deeper look into the philosophy of trial please see these podcasts:
May you always be successful