Basically What's this life except being a huge exam hall where everyday there is a test (Ibtila'); "Do men think that they will be left alone on saying, "We believe", and that they will not be tested?" (Holy Quran). This is the law of Allah in His creation. We are tested in our children, wives, we are tested in our health, disease, we are tested in our wealth, poverty...everything we face or we have is a test for us. Good and evil equally are tests; "We test you by evil and by good by way of trial. to Us must ye return." Holy Quran. And people's performance in the tests are different. We can take a very important kind of Ibtila' which is money; in wealth, some people will thank their God and help the poor and those in need. Others may forget their God and think what they are in is because of themselves and arrogance may fill their hearts. The same in poverty, some will accept Allah's decree, be patient and thank their God and and look for the causes that can promote their lives. Others will not accept it and say "why God?!". Thus money can be a gift or misfortune according to how i act. You said "my gift" or "your fault", i say just let "your fault" away now and lets concentrate on the gift aspect. With my patience, i can turn what i think is misfortune into a gift and with my thankfulness, i won't turn the gift into a misfortune. I can't say that disease in itself is a gift, but i can turn it into a gift. And every thing is good for one kind of people; the believers; "Wonderful is the affair of the believer! His affair in their entirety are good for him: if good befalls him, he is thankful, and that is good for him. And if harm befalls him, he is patient, and that is good for him. And this (prosperous state of being) is only for the believer." Hadith.
Why there is Ibtila'; "Do men think that they will be left alone on saying, "We believe", and that they will not be tested? " "We did test those before them, and Allah will certainly know those who are true from those who are false." Al 'Ankabut, "but (all this was) that Allah might test what is in your breasts and purge what is in your hearts. For Allah knoweth well the secrets of your hearts." Paradise doesn't have a free ticket, but with all kinds of Ibtila', those who pass the test will be rewarded and those who fail will be punished.
The other aspect of "misfortune" is that it's a reminder to return to our sins and faults and revise ourselves; what was the wrong we did? Also, in the time of calamity, i feel that i am weak and no human can benefit me so i don't find a resort except the resort of God and i stand in front of His mercy doors in humiliation and humbleness. Some people don't know their God except in the darkest moments.
So basically the nature of this life is Ibtila' and the most righteous humans i.e. the prophets were the most of humans who tasted Ibtila'.
Thus there are things that happen to us by the decree of God, we don't have any hand in them. And there are things that happen as a result of our actions by Allah's permission.