Happiness is a skill.
"Socially we're told 'Go work out. Go look good.'
That's a multi-player competitive game.
Other people can see if I'm doing a good job or not.
We're told, 'Go make money. Go buy a big house.'
Again, external multi-player competitive game.
Training yourself to be happy is completely internal.
There is no external process, no external validation.
You're competing against yourself - it is a single-player game."
- Lifted from The Almanack of Naval Ravikant - a shorthand guide to wealth, health, and happiness that I just finished this morning.
Maybe that's why happiness is so hard to maintain (as an only-child I am 100% certain that single-player games are not as stimulating as playing against others).
Nevertheless, it's a skill I'm working on and getting better at every day.
How?
By focusing on the present (not future-casting or past-regretting)
Accepting the things I cannot change (and discarding of the desire for it to be any other way)
Gratitude (basic)