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.
I am not 100% sure what you meant there, you are saying that people sold at 4k when the panicked but then you say they did that to buy at lower price but why would you sell BTC at 4k to buy it at 5k ? .. I mean this just doesn't make sense or I am sorry I failed to understand your logic.
I think that such sharp swings in the mood of cryptocurrency users have withdrawn inconsistent players from the market. if someone sold Bitcoin for $ 4,000, fearing for their investments or hoping to buy Bitcoin again at a much lower price, then there were practically no such people on the market. BTC owners today are those cryptocurrency users who have a solid long-term storage solution.