For me the word "steal" in "Good artists copy, great artists steal" quote always meant: make it that good that the public will think it was always yours. The origin does not matter, because reality for people is what they believe in. If you will execute it better than anyone else it will be considered "yours".

Edit: At the same time there are also few options to make people believe it's yours beside exceptional execution, but that's not what the quote is about.