As the title say, what does the word professional say to you? To me it means "I get paid to be great at doing this ".
I would re-phrase it a little bit: "Because you're good at doing something you get paid when you do it". Honestly, I don't think being professional is constant (as in math), rather it's a life-long learning curve. If you're not constantly learning as a professional, you're not going to fully achieve your potential.