Your character might be good at something and bad with other things, but that doesn't mean that he will always use his abilities optimally. He might be overconfident and pick fights he can't win, or too scared to play out his stength.
Literally no player would do that in high stakes circumstances unless the player has no idea what he's doing and what he's messing with. D&D gets very brutal and very real. There high level enemies that pose very real TPK threats and at a tabletop game there's no reloading the last save either. There are enemies designed very intentionally to basically never be messed with and even the most min-maxed of level 20 parties can fall to them if they get a couple unlucky rolls. You spellcaster better not fail that saving throw against the Feeble Mind Spell. Your better be sure you want to mess with disarming the instant death traps rather than walk around them, etc.
Some people act like minmaxing is a dirty word or oh you better not optimize too much or else. But the game is absolutely mercyless. Even with mastery and guidance and everything else stacked in your favor all it really takes is one nat1 roll at the worst time and you are done...permanently, irredeemably done.
