Before now, I also used to think in my head that a professional is determined by how often he wins. Thinking deeper, I don't think these thoughts of mine are wrong, because anyone who wins often is assumed to have mastered the skills involved in gambling. It is not something we see often, so if you can make it happen, then I consider you a professional.

But on the other hand, there is more to being a professional than just winning; A good  risks management skill, bankroll management, time management and every other thing that shows professionalism.