It seems to me that people feel positive emotions when they feel they are 'progressing' in some way. This can be from making more money, getting a nicer car, or a hotter girlfriend.
These positive feelings are usually temporary because you quickly adapt to your new situation or new thing or person.
This is why, for instance, Giselle cheated on Tom Brady; because it was normal to her to be married to him. Whereas a normal woman would do about anything to get with him, she was bored with him and their life.

This also works as things get worse for people. There are levels of descension that are adapted to on the way down to the bottom. A homeless person typically doesn't go from having a stable job and home and then one day gets kicked out onto the street. Things go wrong and become their 'new normal,' which compound and end up with him being homeless and abandoned by his family.

Like temperature, people notice changes to their current mood, and without contrast, people become bored and feel indifferent.
It seems we quickly adapt to things not just physically, like doing a physical task, but also mentally.

Any thoughts?

weak men good times etc

Yeah there's definitely something to that.

This adaption idea seems to make sense, but I don't really like what it means. It implies that what you do doesn't really matter, because it's contrasts in life that are felt, in general.

It would mean that if you're miserable now, you'll feel elated when you stop suffering. If you're happy now, you'll mostly notice when things get worse for you

getting complacent makes it worse

you mean adaptation?