I think it's deeper. The mind is an optimization tool. It always keeps looking for something better, hence it is always not completely happy with the current st

I think it's deeper. The mind is an optimization tool. It always keeps looking for something better, hence it is always not completely happy with the current state of things. The first noble truth (aka the principle of dukkha) is at least 25 centuries old; it says that sentient existence is inseparable from discontent, and thus from suffering. This whole search for a better optimum, like other evolutionary mechanisms, results in survival and proliferation, but not necessarily in happiness. Proliferation seems to correlate positively with happiness, but up to a limit, and the limit is all too visible. On the other hand, reaching the true global optimum does not seem too blissful either: any change would be a change to the worse, so all development, all motion except basically spinning at place would need to stop. This is not very different from death. OTOH the human mind, as it is, would still try to keep on searching, still feel somehow discontent. (I agree that the reasonable path is to try to limit the suffering of living beings, including but not limited to ourselves. It's the least bad option.)