One of the basic teachings of the Torah is that G-d does not expect of a human being anything which is beyond the human capacity to carry out. This is quite understandable, for even a human being, who is very far from absolute perfection, would not expect of a tool that he has fashioned any more than he has put into it. Certainly G-d, the Creator of man, knows man's capacities.
From this, it immediately follows that when a person faces any kind of a test of faith, it is certain that he has been given the capacity to overcome it. And the more difficult the test, the greater are the individual's capacities.
The reason that an individual is tested is not because G-d wants to know how he will acquit himself, but in order that this person be afforded the opportunity to realize his potential, even that which is unknown to him. And when one's potential capacities are released, and activated, they become part and parcel of his or her arsenal, to be used for personal as well as communal benefit.
The stronger one's faith in G-d remains even under adverse circumstances, the sooner it will become clear it was all a matter of a test. But this faith should not be merely a matter of lip service, but must have the full force of conviction.
Some people are born with greater natural capacities, and consequently they are faced with greater challenges and trials. Others are born with lesser capacities, and therefore the challenges and trials that G-d presents to them are also lesser, in keeping with their strength.... If you truly have great trials, this in itself is proof that you possess a great capacity and strength to overcome them.
When it is seen Above that one is strong in one's faith in G-d, and one rises in the general observance of Torah and mitzvos, the test is nullified and there is an increase in blessing, salvation and success.
Source: Excerpts from letters written by the Lubavitcher Rebbe.