Well, if we knew where and when, we'd be billionaires.
Like this, we only have to regret what we did or what we didn't do 🙂

I buy for 100. if it starts to fall, I let it go, even if it falls to 0. If it starts to rise, I'll wait until 150, then sell for 50, so that I can buy it again if it falls below the entry price... But this happened very rarely :-)