[binbag]

This is extremely obvious and it’s what you think it is.

[brocha]

Most people don’t think along this axis. It’s the same reason why if you asked somebody how a toilet works or the functionality of P-trap (both things a majority have interacted with/seen more frequently than a plane window), they’d probably give you a blank stare.

[nehal3m]

I guess it is to most people, but others have never given it an iota of thought and some are part of today's lucky 10,000! https://xkcd.com/1053/