Why do some people want to hold the same stocks for (possibly) the duration of their lifetime/work life time?

I keep seeing this sentiment, that people say they don't care what the stock price is as they intend to hold it for 20 years or longer. If this were a person above (as an example) 50 and is mainly interested in dividends, then I could understand, however I see this attitude from plenty people under 35. And this I don't really understand.

I for example tend to place stop losses when a stock of mine goes above 80%+. I did this with ASML and AMD recently, both which were way above 100% plus since I bought them and the stop loss triggered recently. I am fine with this, the thinking being that I rather take home the 100%+ gain now, pay the taxes and then look to reinvest into other stocks. Because this way I have guaranteed that I took the winnings home (and if I sell later, I am still paying taxes then).

If the stock goes from 150% plus -> 0%, then what have I held this stock for (note ignoring various possible justifications for this like dividends)? Yes the stock could go from 150% -> 0% -> 300%, but no one knows that. All I know is that right NOW the stock is at 150%, why not be happy with that and use the opportunity to find something else?