Why aren't billionares happy if they have tonns of money and can afford to do absolutely anything? The answer lies in relativity.

When planning on doing something, we create expectations. If those expectations are exceeded, we feel happy. If the actual experience falls behind the expectations, we feel depressed. Once we understand if our expectations were too high or too low, we subconciously regulate them onto a more realistic and preferrable level.

This leads towards some popular psychological advice: "Regulating your expectations is key to a general feeling of happiness".
Problem is, we aren't really the ones who create them. We don't choose which expectations to have.

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