It's the same with reading, give me a book I like and it's done in days, give me one I don't and I may never finish it. Story telling is the oldest art form in the history of mankind, before we had an alphabet we passed our history from one generation to another through stories. If you are hearing or telling one that is meaningful to yourself then it's nothing like work.
It's almost as if the words just flow through you so easily you don't even think about it. It's when we force ourselves to create, when there is a deadline on our creativity, for if the subject holds no interest for us at all things become stagnant. I used to get in trouble for twisting the subject matter on written assignments to suite my way of thinking lol. I have a way of making things fit where I want them to, that's what being a wordsmith is all about. It gets me in trouble with work from time to time, but I can't change the way I think or tell a story ;)