Here's a thing that happy people know, whether they consciously know they know it or not: they know that happiness is an entirely subjective reality. That happiness is quite literally in the eye of the beholder.
They know you can always find something to complain about, even at the best of times. And they know there can always be something to appreciate, even in the worst of times.
In the best of times the sun is shining, the water is clear, the kids are happily entertaining themselves, the Pimms is chilled and the stomach is looking pleasingly flat. But if we try hard we can see that there are endless flies, there is going to be so much cleaning up to do, and why the hell can't people put stuff away once in a while?
In the worst of times the mortgage is stretched. Each day is a marathon of endurance, putting on a smile to give the semblance of coping. But if we try hard, hard, hard we can see the smile from the barista making our coffee just so, the lucky parking space that appeared just like magic, and be grateful for the friend who gave us a call just because.
Happy people look for things, actively seek out things to be happy about and to enthuse about. And then they dwell on those things. They behold the positive even if it's trifling.