Funny, I've always thought that a good relationship required two healthy, sane and happy people to have a chance at staying together.
But we do not live in a perfect world, and no-one is perfect. Having spoken to people whom can only be considered damaged, and noticing how even the healthy couples have their own problems, I think I got this wrong.
A good relationship is when you both weather bad times and troubles. If it were just about the happy and nice times, then you'd be in disneyland.
This doesn't mean you should just stay in a dysfunctional relationship. It just means that if you can share your troubles with your partner, you can actually grow through them together, which is much more satisfying (And a stronger bond) than simply having had fun.