>>26123 (OP)
We are mammals that up until recently had very different lifestyles. Hunting/Gathering, being exposed to the weather, scouting for predators and so on. Depression is a decline of the nervous system due to lack of stimulation. (just like muscles decline if not trained)
The human mind adapts to the status quo rather quickly, even when you win the lottery you'll get used to it.
The problem of today is that most struggle is psychological rather than physical.
Like >>26139 I recommend you to read kacinskys manifesto, aswell as a bit about neuroscience in general. It'll give you a bit of insight about the human mind.