Fun has been a theme in Haikyuu for a long time see: Tsukishima

Fun is also heavily tied to the concept of being good

Oikawa is someone who dims the fact he is "good", he deflects it even if he is objectively good

In Haikyuu there are characters who get good because it's fun. And there are the others who later find fun because they get good

And then there's oikawa, that weird middle, who is good but probably doesn't think so (HES PLAYING IN ARGENTINA GUYS. That's... A hell league. Good is always a relative stat), and who probably doesn't let himself have fun in the pursuit of good

Part of Hinata's development is learning that the un-fun things leads to being good. Investment of one's current enjoyment for the later payoff

Contrast Kageyama whose childhood wasn't Normal (sacrificed fun) but Hella beast on the court now, having the time of his life

Enter Sakusa, someone not doing it for the fun at all, wandering to volleyball by chance but finding meaning and satisfaction in it. Fun as motivation isn't everything

Enter Atsumu, our favorite copycat. He tries things out of curiosity, purely because it's fun and interesting. He becomes a setter because he watched a good setter and latched onto it. Exit Osamu later on, whose skills are on par but fun level is not the same.

And so, circling back to Tsukishima. Volleyball is fun and has been since he got good. But he finds other things fun and interesting. Which is why he pursues other things in parallel :)

And so: do what you love. Love what you do. Do both. Do either. Have fun. Life's not that deep. Haikyuu is great.