
Is a professional someone who does his work even when they do not feel like doing it?
A professional is one who does things even when they do not feel like doing it.
Someone who treats writing like a hobby may write only when they feel like it or enjoy it.
A professional who treats writing as a career, writes no matter what state of mood he or she is in and get things done.
What do you think?

Note
* Thanks C.G and The Niche Man for reminding me of this answer I had some time back.