I disagree with this slightly. There are way too many amateurs who think they’re professionals when they aren’t. There are also too many professionals who behave like amateurs. ‘Being professional’ doesn’t necessarily mean published for the world to read. Some of the most brilliant writers have yet to see publication. A lot of time ‘being professional’ is how you handle yourself within the writing community. It’s a small community, even if it seems quite large. People talk. You want other writers to speak well of you, even if they don’t personally know you.