Watching the movie "Happy" and thinking about what actually leads to contentment explained something that had previously been a mystery to me. When I'm in a terrible mood, I can always cheer myself up by going out and picking up trash from the woods around the pedestrian/bike paths near my house.
This has always seemed counter-intuitive. It should be annoying to clean up after someone else. I should feel I'm abetting their neglect and lack of courtesy. Also, I've already paid my portion of the salaries of people whose job it is to pick up this trash - why am I having to do it myself? Usually, when I tell people how much better I feel after picking up trash, they respond that they wouldn't find the experience fulfilling. on the contrary, it would piss them off.
All I can say is: try it. Yes, I have flashes of annoyance at people's carelessness while I'm working, but dumping out a bunch of trash at the end is incredibly fulfilling. The woods look nicer and I feel better. I don't take pictures or beg for applause on social media - no one in the neighborhood knows at all. Its value is totally private.
One of the three areas correlated with happiness (according to the documentary Happy) is the feeling that you're making a difference in the world. It turns out that my trash-picking is just a simple means of honoring that human need, graciously made available by the folks throwing their gatorade bottles into the bushes.