everyone will surely regret it if they have gone through times of altcoin bulls reaching new ATH and has been followed by a correction. because the new ATH is unlikely to happen in the near future, but it takes a long time. and if we can sell altcoins on new ATH then we have a chance to get bigger profits. and we can buy it back when the correction occurs.
Taking profit during bullrun is good because you can enjoy your earnings. We'll never know when might the price decrease again after reaching the ATH thus to avoid having regrets dont refrain yourself from selling if thats what you think the best for yourself. But there are investors who are firm to not sell even the price reach the ATH then turns downward again These people are determine to keep holding until the price reach their desired value to finally sell.
Yes, better to take profits on each milestone rather than waiting for our dream all time high. Bitcoin is a market that usually dumps 70 - 80%, so if you did not take profits you will regret your decision later. However there are few people who do not want to sell for a very long time like 10 years or more, that's also a good approach if you are not active in trading.
wow if anyone sells cryptocurrencies over the next 10 years maybe they are very rich people now,
and indeed it is cold money, but for everyone who invests in cryptocurrencies I sure don't want capital to be lost,
so my advice is don't hold up to 10 years, but trade 10 years!