What ""common knowledge"" is actually completely false?

People always go on about how we only use 10 percent of our brains, which is just plain nonsense. If that were true, most of the guys I work with would be walking around with half their heads missing and still get the job done, but that’s not how it works. Every scan shows that almost every part of the brain has a known function and is active throughout the day, even when you're just sitting there having a coffee.

Another one that really bugs me is the idea that you have to wait an hour after eating before you jump into the pool. I remember my old man drilling that into my head when I was a kid, making us sit on the sidelines forever. Honestly, I've jumped in plenty of times right after a meal and I'm still here. You might get a little cramp if you're doing heavy laps, but it's not like you're going to just sink to the bottom like a stone.

And don't even get me started on the whole "shaving makes your hair grow back thicker" myth. I've been shaving for over two decades now, and let me tell you, if that were true, I’d have a beard thick enough to stop a bullet by now. It just feels coarser because you're cutting the hair at the blunt end rather than letting it taper off naturally. It's just one of those things people keep repeating until everyone thinks it's the gospel truth.