Well, everyone can profit from that saying, the trouble is not the saying, it is the fact that people can't do it. When bitcoin crashed to 4k in march, people sold because they thought it would go lower, hell some people actually sold so that they could buy a bunch of bitcoins lower. What happened? It went higher.

It means people fail at realizing "buy low" part of it, of course ton of people understood it correctly and bought, which is why bitcoin price went up. Sell high is also not something they understand easily, it was over 10k and not moving any further up, moved all the way from 4k, what did people do? They waited for it to go to 20k. So they failed the sell high as well. In the end the term "buy low, sell high" is correct, it is the people that fail doing that.