What makes a Professional, Pro?

I've often wondered this as I come across many professional people in my day to day life. What does it mean to be professional? Is it the amount of hours you put into the craft? Or is it a degree you achieve with a finite amount of schooling?

Here is what I think. It seems from observation and experience that its a multitude of different aspects that make us a professional. Sure it helps to have schooling and a degree, but I think the most important aspect is time. Some professionals such a Albert Einstein dropped out of school early but achieved immense accomplishments by dedicating years of trial and error to their craft.

The other thing about be a professional that people get stumped on is the fact that you don't always have to be right. Mistakes are a part of learning; it's what differentiates between someone who is wise and someone who is arrogant.

Here is an example of what I mean. I've been a macro photographer for 5 years, I am self taught, and I don't have a degree. Some people may view me as a professional based on my work and time in the field. Others may disagree and say you must have a degree in order to become a professional in your career.

What do you think attributes to becoming a professional? Let me know in the comments section. Thanks for reading!