Why you should blame yourself after every loss
Pretty simple really. I'm not going to pull the "what's the only constant in all of your games? You" card, because that honestly makes it seem like the variables affect nothing. But, there are some pretty big benefits to blaming yourself for your losses, instead of anyone else. Even in games where you feel like you played absolutely perfect, go through and watch them again and find anything you can fix about your performance.
Why?
Your performance is the only one you can control. If you focus on "This bot lane keeps pushing and dying to ganks!" or "we keep getting ganked and no one's helping!" then you're not improving anything, except maybe making yourself more tilted. Instead, focus on how you can improve next time.
Top: "I should tell bot to ward, so if they get ganked I can make a TP play." or "If bot gets ganked, I should match pressure top so we at least get something out of it." Jg: "I should get some wards down bot so they can see a gank coming, and I can respond faster if they get ganked." Mid: "I should try hard to push lane so enemy mid can't gank bot," or "I should try to get some wards in river after I push the wave," or even "I should try to roam bot to return a gank after pushing this wave." Bot: "We keep getting dove, so we should invest more in items like cull and wards so we can see ganks coming and try to set up a method for allies to come help."
Etc.
I know sometimes it'll seem outlandish, and you'll want to blame your carry who fed instead of doing their job or something like that. Sometimes you'll think you played absolutely incredible that game, and honestly, maybe you did. But if you focus on others' mistakes instead of trying to improve your own play, you won't be making any actual progress.