- The amateur practices until they get it right.
- The professional practices until they can't get it wrong."

How I wish this was a bit more true than it actually is. I really dislike the definition that says if you get paid for it you're professional.
When I was younger and learning music, if I got something figured out that sounded really good, I'd say, "wow, that sounds just like the professionals." We still talk about things having a really professional sound. To me the word still implies a mastery level of skill and artestry. If getting paid was the only criteria, then I better stop saying that this or that sounds like the pros. Because there are some really horrible professionals out there.