How are people not constantly angry and sad at the world?

I already know I’ve got depression issues. What I’m wondering is how to look past all the ugly things and live in a generally happy way.

I see lots of good in my life, but the bad is so overwhelming it nearly wipes all the happiness away. How do you cope, or appreciate the good things more? There’s got to be some mechanism that separates the optimists from the pessimists. Do you know of such a thing?