I ran into a question online (on HubPages) that asked (essentially) what the title of this post does. This is the reply I posted to that question (since on HubPages one never really knows if his reply will be, or remain, posted; and I figured my "thoughts on the matter" would make a better post on here than not posting anything.
I don't necessarily think some "adversities" (or just "generally bad things that happen") are the things that contribute to someone's eventual success or general well-being. I think in many cases people either go into what the the bad thing is with a healthy perspective and ability to figure out out to cope, how to to manage the thing (and its consequences), etc.; or else people unprepared for some types of "bad things" are hit with them and didn't have what it took in the first place to survive them.
I think it makes a big difference how old someone is, how responsible for other people (like their children/family, for example) they are, how much their "bad thing" has affected them, etc. And, I think WHAT the bad thing is/was makes a big difference too.
Some bad things prepare people for other bad things, of course. So, I suppose, if one or another type of bad thing isn't so devastating (to the individual and/or his family) some bad things can make good practice for others that may follow. Some may knock people's whole lives for such a loop that they affect more than just the individual. Sometimes the person who must make accommodations because of the bad thing must make less-than-ideal choices (like taking a job away from one's once promising career in order to support children).
How much of one's "identity" one has built on one area of life or another can affect how devastating a blow any "bad thing" is too.
Then, too, what shouldn't be overlooked is that some temporary and apparent set-backs don't mean the person hasn't gotten past them. - only that he hasn't gotten past them YET. Sometimes, too, if the person didn't care all that much about the particular failure in the first place, he'll just not bother trying to do better at the same kind of thing, particularly if the person has other areas of interest, talent, or mix of priorities in life..