Newish to stocks. With Nvidia’s increase today, is it smart to sell?

I don't want to miss my oppurtunity, as I did yesterday with CohBar (which went from +40% to -20% for me). I've had the Nvidia stock for a few weeks, but now is the first time its at +30% (total percentage of change). After yesterday, I told myself that I'd sell anything that hits +30% again, but I didn't expect that to happen again today…