What doesn't kill us makes us stronger. Friedrich Nietzsche. Facing challenges and adversity makes us stronger and makes our lives more interesting. This is true on a smaller scale and a larger scale. On a smaller scale even doing various types of crossword and mind puzzles increases our memory and brain function. Bigger challenges make us stronger and more resilient throughout our lives.
I didn't actually see it, but there is supposedly an Oprah episode where a depressed woman jumped in front of a train and had her legs severed. Once she recovered, she was no longer depressed and feels she lives a happy fulfilled life. When I first heard this, I was surprised, but I've heard similar stories since and am less surprised ever time I come across them. It seems adversity can also make us happier.
There is a study where researchers found that the period of time prior to a vacation makes people happier than the actual vacation does (http://www.smartertravel.com/blogs/today-in-travel/study-shows-people-happier-before-not-after-vacation.html?id=4403288). I can't find an online article about it, but there was also a study a while back in a psychology magazine about people being happier working on a hard, arduous project than they were upon its completion and reward. I think both of these things point to attitude and positive thinking. It's easier to have a positive attitude when you know something good is coming up and so almost everyone is likely to do it and be happier. It is harder, but just as or more important, to have that positive attitude when adversity strikes.
I think that overcoming difficult situations is important to our happiness. Even in watching movies, we often feel a sense of exhilaration only when the hero or heroine overcomes something dreadful. The worse the awful situation the happier we are at the end of the movie and movie makers sometimes do a great job by capitalizing on this. I know how hard it is to believe this and if someone tried pointing this out when I was driving to move back in with my mom when my first husband and I were going to get a divorce I would likely have not had anything kind to say to that person. I do, however, strongly believe that without that divorce, I would likely still be pretty miserable and my current marriage wouldn't be as blissfully happy as it is.