How i see it, there are 2 ways of looking at things. Either they suck, or they're good. And it's a choice you make, because things don't MAKE you unhappy, you CHOOSE to feel that way. Either you see things as a cup-half-full or a cup-half-empty.
It's not about your nature either. You can teach yourself how to view everything with a positive spin, even if you've been a pessimist all your life. You can teach yourself to tell yourself that it isn't as bad as it could be, it could always be worse, and to take whatever comes as an opportunity to learn, grow, become stronger, teach someone else, etc...
Let's face it, life is a gift. You were lucky to have gotten this far, and millions haven't. You can make the most of it, or wallow away in despair and give up. You can whinge and whine and make yourself feel even worse, or you can believe in the future and turn your situation around.
The cup is filled to same level, no matter how you perceive it, but i can tell you that if it's half full, you'll take great delight in rising to the challenge and turning any weakness into a strength.