I've noticed that I sometimes have this problem. However, there's a bright side that makes it slightly easier: I've found that generally if I have a pragmatic reason to enjoy someone's company that's generally some major positive trait (e.g. only expert on a certain topic around me, is a better chess player than anyone else around, is the only other Go player around, etc.) This provides a positive trait to start with.

The whole thing about the understanding that other humans have circumstances that help explain actions also is something that's been nagging at the back of my mind for a while as somewhat similar. The phrasing here about using it to actively assume that people had good reasons for their behavior made it click more. There's an old tradition in Judaism about trying to assume that people mean well and when one sees something negative one should assume extenuating circumstances not apparent to you. This idea was heavily promoted by among other people the Chofetz Chaim (he was a major Rabbi living around 1900). Sometimes this sort of view was pushed to points where something is just actively anti-rational (ridiculously contrived stories are sometimes told to Orthodox kids to inculcate this point). This also results in some very bad attitudes in the ultra-Orthodox population about not willing to accept that someone did something wrong even when there's heavy evidence (curiously this attitude occurs primarily with people of very high status). This leads to a general worry here: is the effort to try to think of explanatory circumstances here possibly against good rational thinking? In particular, there seems to be a problem if one tries to deal with the fundamental attribution error only when they are people you have a reason to try and like. This seems to easily lead to tribalism. (And again, using the comparison to Orthodox Judaism, these sorts of assumptions are essentially never applied to people outside the fold).