I am generally happy all the time, until someone says or does something that unsettles me. But the older you get, the more you realize that you're in control of how you feel. So just by tuning out certain things, you automatically start feeling happier and better.
I'm told there's some buddhist philosophy behind that. I wouldn't know. I'm not a buddhist.
There are some things and some people though, that when they enter your life, really do boost your feelings.