Faustian Spirit
Gon, Killua, and all the hunters in general are prime examples of the Faustian Spirit. The Faustian Spirit basically means using all your potential to achieve something great and to deeply pursue or explore it in ways ordinary people won't. The entire point of being a hunter is chasing after that greatness in any field. I really, reallyyyy like Killua's character, not just because of his character development throughout the series, but also for this Faustian Spirit. Like, the incredible potential of Gon and Killua is frequently brought up in the story and the fandom, but one thing we all can learn is to utilize all our potential to achieve greatness in everything we do. To reject being average and strive to be the best and give it our all.
Enjoy life. Work hard but play even harder!