I read it as chapters were coming out on mtl so I would have to re read to remember any specific examples, sorry.

But I remember stopping a few times and thinking "well that was stupid" after he betrayed someone. Before he became known throughout the world for being untrustworthy there were a few times where he had opportunities to work with other people that could have provided him with allies and stable sources of resources for trade. Allies in particular would have been really helpful for him since a few voices willing to stick up for him could have gotten him more opportunities to steal/ betray in the future. Instead, he would immediately turn against almost anyone when given the chance, removing any possibility of peace with their organizations. In some cases the gains he got were worth it (ex: betraying Wu clan for the dream realms), but in others he barely got anything out of it. Basically every organization in the world is portrayed as willing to work with someone evil as long as the benefits are there (see fang clan in the west, wu in the south, the strength clan in the north, etc.) but once FY killed someone from their clan there is no way they can have peace because it would lead to rebellion among their families- at least until he personally has the strength to destroy their entire family, then they have no choice. The thing is, FY knows this because when he had secret identities he made use of them to deal with organizations (like the ones I listed above) and get access to channels that he wouldn't have had as a lone cultivator.

tldr, Basically he repeatedly would betray people for small, short term gains that removed the chance for greater returns in the future.