“You don’t know what you can do. You won’t know until you try.”
“you don’t know won’t hurt you. A dubious maxim: sometimes what you don’t know can hurt you very much.”
“You never know just what you can do until you try.”
“Until you try, you don't know what you can't do.”
“You never know how much you can do, until you try to do more than you can.”
“You don't know what you can get away with until you try.”