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It's not that easy of a mindset, OP if you even care. For newbies, the usual term "FOMO" becomes common to them when it comes to those situation. Whatever ROI that they had missed due to another ATH caused them to panic to immediately buy because why not right? It keeps them thinking that there will be another ATH. Don't believe me? It came from my experience when I was still starting in crypto and it was a truly horrendous experience.
Good thing I wasn't fully committed yet to crypto that time.
For newbies the situation really becomes very worst some time because they often invest in scam coins with in the rush to get the profit. They often do these regrets and they often miss. But with time they learn to remain calm and do not rush and they then watch everything first then learn and after that take decision.
I guess not just in crypto, but in all types of investments, we often create wrong decisions at first but as we go on, we learn to understand why did it happen and becomes more calm and watchful on the market. Yes, the given situation will really make us to feel regrets because we miss a good chance to sell, but does regretting helps us in another way? I guess no. So we should change our mindset and just be contented on whatever profits we have at the moment and just sell. Crypto is unpredictable so there is no guarantee that we can make more profits in the next days to come, especially if the market suddenly crash. So as much as possible, sell when we see good opportunity to make profits, as long term hodling is not always profitable in the long run.