There's also an issue regarding not wanting a character to be bad (or, as an extension of that, having them be really good, or even "the best") in one particular area.
The best example of this that I've ever seen is someone who wanted to play a "halfling titan" character in D&D 5E. The idea was that their halfling was so strong they could put even a goliath bodybuilder to shame. The problem with this is that D&D 5E limits a PC's Strength (and that of most non-monstrous NPCs) to 20 which means that, for some sort of opposed Strength content (e.g. arm wrestling), it's going to be effectively a random roll. (Plus, for something like comparative lifting, the goliaths will still win, being Medium creatures with the powerful build trait.)