What makes this game change peoples personality?

The game is competitive, you can see that even in normal games. I, too, change when playing league, I get mad at every mistake i see, but there are even worse. I won't say i never had a nice game where my teammates didn't feed, but there are players that break at 1 death. Mainly yasuo in low elo. You see a yasuo get first-blooded? get ready, it's not over yet.