First GF didn't like me hanging out with my girl & guy friends, took a long time to reforge those relationships afterwards & some were non-salvageable. So, that went on the list.

Had a fling with someone who lived on an incredibly limited budget and had no intention of changing it, totally fine with no money for "unnecessary" things (holiday, meal out, etc). Short fling was enough experience to tell me I couldn't hack that long term. So, that went on the list.

Had someone who chased Likes seemingly more than my opinion of her. The photos got more and more provocative as time went on. On to the list!

Another disapproved of my gaming habits. Sort of a "do that shit when I'm not around", which did work... until we got more serious. More time together meant less time to do my own things. That relationship broke down once we started getting serious because I didn't have time to do my own hobbies.

... Btw, these weren't necessarily the reason the relationships ended. Most of them ran their course, these were just some of the small lessons that I took from them, to try and make the next one work a little better.