Honestly the player character can be A LOT of things...and an Intelligence of 19 or 20 is basically equivalent to having a 200 IQ...then there are the skill monkeys with a billion proficiencies where realistically a religion check could tell you what's up or an insight check could tell you she's not honest, etc. etc. etc. There are a lot of ways in which a custom character could figure that stuff out...unless you made a barbarian who only understands the word smash.
