The biggest problem of todays society is greed, even when people are doing good profit from a coin (50-70%) they are not selling them. They keep holding all their altcoins and sooner or later the price drops and makes -x10.
this happened to me in the past when I bought ETH, at that time the price had increased but I didn't sell it immediately because I was sure it would go up again but what happened ETH went down and I regret that I didn't sell it when it went up and now I if I do trading if it's a profit I will sell it immediately for fear of repeating again like before
The market is the best teacher of all time, no one can guide you to find the perfect entry and exit price points. The greedy human psychology is the reason behind the flash crash and monthly uptrend on the crypto charts, it is same psychology in other financial markets. If you missed the trading opporutnity, don't overthink about it, another opportunity will shine on the corner.