When to sell that great stock?

I think a lot of investors/traders do a pretty good job of picking stocks that go up in value. It does follow the general market trend in the last few years. But, I've seen, and been victim of, following that stock right back down after it goes up. Failing to sell at an appropriate time. I mean, how many BTC millionaires were made and then lost before they cashed out? Is there anything you use to determine a good time to sell? Day traders often use a 2x profit which doesn't apply to investors. Or does it? Maybe you use RSI if you're on the technical side? Or a trailing loss percentage? Tons of info out there about when to BUY a stock (technicals, fundamentals, sentiment). But, what do YOU use to determine when to SELL one?