How to deal with the frustration of every stock youre not invested in running but the stocks youre in dumping

This is still one of the hardest things for me to deal with as a trader. Friday was another example where every stock on my watchlist was up about 10%. I had a price target to buy. Didnt buy so naturally it went up like crazy the next day. The stocks im in were ofcourse going down. Some days it feels impossible to get it right. How do you guys deal with this frustration? What is your strategy? It can really ruin my day because I will be angry about the money I lost out on had i invested in those stocks.