I first saw this on a bus placard in college, Kent State, (yes I was there in 1970 but let me tell you about it some other time) and it has stayed with me. That and a Mark Twain quote that goes roughly like this, "If you wish to be a writer, write for two years without pay. If at the end of that time, no one is willing to pay you to continue, take that as a sign that sawing wood is the occupation for which you are intended." I have transposed both to painting.
Teachers, even some I respected, tried to steer me to writing. I don't flatter myself that I had much talent for it, they probably do that with anyone who can put together more than two words. I consider English to be my second language being much more fluent in images: other people's paintings, photographs, motion pictures. Like Maggies Libby sez, "What a strange thing to deal in!", but I am stuck with it.
There was not even a nod in the direction of visual literacy in public school; I was tracked for college and was not allowed to take art in any form; a frivolous waste of my time that. I was finally able to sign up for studio art classes in college but with that came attitude. "What do you propose to do with THAT?!! Teach, I suppose". Even there, as I say about all my formal education, I managed to learn in spite of it, a library card being the key.
So I say, "If you want to be a painter, paint". Don't talk about being a painter, don't read about being a painter, don't think about it, fantasize about it, write about it, whine about it. Just paint.