Does it bother you when your significant other squeezes the toothpaste tube wrong, or puts the toilet paper on the roll wrong? You tell yourself those are little things that shouldn’t matter, but it still gets under your skin.
Elliot Mason wrote a little song about it, with a wacky video. -via Arbroath
https://en.wikipedia.org/wiki/Normal_%28geometry%29
It sticks out from the wall instead of being parallel.