My dad taught me to play tennis when I was younger and then I went on to play for my school. I still remember early on as a teenager getting incredibly frustrated, angry at myself, etc, and this was his advice, which stuck with me: "15 steps. You've got 15 or so steps to be angry, but when it's time for the next serve, it's over."

It's okay to be frustrated or upset while playing, but there is a difference between being frustrated and getting so wrapped up in your frustration you start to make mistakes. Because that's what will happen. When I "play pissy" as my dad would say I would always end up losing to him - because he would see what made me angry and do it over and over.

Another thing that cleared my head a bit was in high school playing against someone with a TERRIBLE temper. As in show quality levels of dramatic. After I won they broke their racket, threw it across the court, and wouldn't pick it up - a teammate came to reclaim it. I never got anywhere near that angry playing, but for some reason watching that shitshow made me considerably calmer as a player after that, haha. Nice to have perspective I guess.