One realistic thing that people seem to gloss over in gaming is religion. Yes, there are clerics and paladins and whatever, but the religious beliefs of PCs, particularly in culturally pre-modern settings, gets short shrift. Religion is extremely important to history, and was generally very important to individual people until very recently. We live in a mostly secular era and I think we have a hard time modeling how powerful something like the threat of excommunication could be.
Probably because they think of interactions with real deities as transactional rather than spiritual? Or they just aren't spiritual to begin with? Not sure.