> But on the other hand, people with really low expectations are usually not super happy when something turns out better than expected

I don't know, in my experience having high expectations seems to set you up for a higher fall and a lower upside, thus leading to less happiness. I have generally quite low expectations and am generally quite happy. Some people around me have generally much higher expectations and are generally quite unhappy. The things in life where I do have some higher expectations about are also the things I'm the least happy about.