How often do you write a question or answer, and delete it before ever hitting the button to post it?

I just wrote three answers the collective will never see. I deleted them before ever hitting answer. I probably only do it about 5%-10% of the time on answers, tonight was a rare occasion having so many. With questions I think I do it more like 25% of the time.

What about you? What makes you erase instead of post? Once you write it out do you feel like no one will be interested in your answer? Or, do you realize you did not answer the main question. Or, that you have just revealed too much of yourself and thought better of it?