Most writers write for professional reasons, but then there are an overwhelming lot of people who dabble in writing due to personal reasons. Writing for them is a catharsis, a purging of pain from the soul, a detoxification of the spirit.
There are times when a professional writer may be forced by a crisis of the soul or of physical circumstances to resort to writing as personal catharsis. The results are sometimes masterpieces of creative art or incoherent rantings. I suppose the quality of the cathartic product depends on the quality of the writer!
Sometimes when I am tempted to rant, I give in to it. I then preserve what I write. It is interesting to read them after much time has passed. Some seem hilarious after a time, other puerile, and some still move me to tears, even after years have passed.
It is the last which have the potential to inspire for some true writing.