When I was in medical school, one of my classmates made a list of things that you need to be happy. He actually put a lot of thought into it and made it into a very comprehensive list.
I don't remember much of it, but it contained the usual suspects. You need a significant other, a career that you enjoy, and the ability to be able to enjoy good food.
But number one on the list was:
Being able to pee.
Because he figured that if you couldn't pee, then you couldn't enjoy any of those other things.
(What specialty do you think this guy went into?)