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Adding to that, I'm reading Antidote by Oliver Burkeman. One of the points that I really related to was that more you think about happiness, more likely you will find yourself unhappy. Essentially the pursuit/expectation of happiness paradoxically will make your brain think of all the things wrong in your life. I don't know how it started, I think that's been true for me. I never thought about happiness when I was young. There were things that were not perfect -- not enough money, no girlfriend, not having clarity on what to do next, failures, envy in general -- but I was still much happier relatively and I was by no means thinking about happiness back then. Just accepted it is what it is, and kept going on with life.