The point @
Manbearcat is making is that many parts of D&D magic
are explained. For instance, the wizard has to copy spell formulae into his/her spellbook. And then has to read those formulae. And then, at least in AD&D (I'm not as sure about 5e) has to impress the mystic formulae upon his/her mind. Then, when casting, s/he has to speak certain words perfectly, and wiggle his/her fingers in just the right way, and pull the right material component out of his/her pouch at the right time.
If a player wants his/her bard to sing a song perfectly, a Perform check must be made. Why does the player of a wizard character not have to make a Perform check to recite the words of the spell properly?
If a player wants his/her thief to do a card trick without fumbling, a Sleight of Hand check mut be made. Why does the player of a wizard not have to make some sort of DEX check to wiggle his/her fingers properly, or to pull the right component out of the spell component pouch?
To remember facts requires an INT check. So why does forcing a spell formula into the brain of the caster not require an INT check also? Why does transcribing a spell into a spell book not require an INT check to avoid confusion/mistranslation (as a real-life teacher of complicated material, I can say that transcription by students is far from infallible), or a DEX check to get the copying right (I know more than one person who can't read his/her own handwriting)?
And flipping this around: if we are happy with a mechanical system that ignores the chances of a wizard mucking these things up, and that allows auto-success whenever the player makes the action declaration "I'm transcribing a spell", "I'm memorising a spell", "I'm casting a spell", then what is wrong with a system that similarly ignores the chance of a fighter or rogue mucking things up when the player declares "I'm cutting down that goblin" or "I'm hiding behind that tree/ogre/person." (DoaM would be an example of such a system. Some of the 4e powers for rogues that let the turn invisible etc are similar such examples. Others could probably be invented without much trouble.)