An old psych study claims that one year after some great or terrible event, winning the lottery, or breaking your back. People are roughly as happy on average as they were before the event. It makes sense in many ways, happiness does not seem to change much over life. To me it looks like happiness is regulated towards some fix point. This is often cited as a reason not to despair, which is nice, but for someone like me it is horrifying. Much like with weight, there is no reason to assume that you are being regulated towards a healthy state.
I am successful by most metrics, but I am so despite being miserable, and well aware of it. But it is also a question of what kinds of tasks I focus on, positivity and natural happiness is extremely important for most sales people, and beneficial for teamwork, especially high stress teamwork. But less so for solitary independent work like research, and too much positivity seems to make people easier to scam, and I would prefer a cynic as responsible for it sec (not that I have ever seen one that wasn't). Happiness has a wide range of other positive effects too, but it is difficult to decorrelate, and if I was optimistic Id say something like teamwork and sales are easy to measure, so anything which is positively correlated with work productivity will be biased due to selection bias. If I was pessimistic I think Id just say yeah its probably true, but hey, the world isn't fair, and while I am miserable, at least I'm not stupid, and I would not want those two reversed.