Sometimes when i just stand completely still, and i scope in on the enemies head and tap once, the bullet hit a pixel behind him and doesnt register, why does this happen, the enemy is standing still too

An old drawing of Killjoy. From a contest that I entered a while ago, and I would like to show you now. I hope you like it as it took me quite a long time. I wanted to try the style that Valorant wears, but clearly Valorant's art is superio...