"to reinvent the wheel" = spending a lot of time trying to do something, when that thing has already been done. Think about a wheel. It's round, right? Could you design a better wheel? Probably not. No matter how much you thought about it, no matter how much time you spent, you couldn't "invent a better wheel." So why bother? Just buy one from the store. Same concept. Don't bother trying to figure out how the best way to learn a language. Just do what the experts do.