“You know, I really don’t think you learn from teachers. You learn from work. I think what you learn, really, is how to be – you have to be your own toughest critic, and you only learn that from work, from seeing work.”—– Garry Winogrand
Urban Development in Panama
Lingua Franca 
That’s a great — and true — quotation. Teachers are important, but becoming our own teacher counts, too.
John Dewey, a well-known teacher, promoted “learning by doing”. He nailed it with this quotation as well.