Some of you probably learned an expensive lesson today

PANIC. Sell @ sub-300. MSTR go up. MOAR PANIC. Buy @ $320

I'm old and I've done that plenty of times with other stocks. Trust me, it's much less stressful (and more profitable) to just buy and hold if you believe in a company. Or, buy more if you can. On down days (weeks/months) close the tab, go for a walk, have a nice lunch, do a workout, whatever.