Strange has already mastered all of the Cincinnati Chili Enjoy It With Crackers Shirts that can be found on Earth. He has also learned magic and magical principles from other planets and other dimensions as well. During one of the periods he was without magic, he traveled to other worlds to relearn magic from other planets whose rules were completely different from what he knew here. Stephen’s intellect should have never been in question having been a member of the secret cabal of the Marvel Universe’s greatest minds and most formidable leaders, the secretive Illuminati. He doesn’t just learn the rules, he then learns magic to violate causality entirely creating feats of magic which defy those rules, not just here but in any reality he can use magic in. Doctor Strange has to study reality itself, not just where he lives but all of the adjacent realities next to ours. He makes an effort to understand the species who live there, what drives them, their societies, their technologies and their magicks.