Isaac's briefest manifesto ever:
The ultimate purpose of art-- particularly writing-- is not self-expression. Self-expression is, in general, what art is made out of, it's base materials. But like how a wooden table's purpose is not to be made of wood, art's ultimate goal cannot be to be self-expression. It's already that. That's where it begins (most of the time, broadly speaking). It must do something else, something more. One of those things, preferably, is to give something to the reader. If that something is the experience of what is going on in the writer's head at that moment, the question becomes why this gift is worthwhile. If you are only writing for self-expression, just get a fucking blog.
Thumbs up to that. Since art is not self expression, what it is is communication. That's why self-expression is the raw material: what you want to get across, the idea or experience (whether it's a concept or a feeling) you want to transmit comes from you, but is aimed at someone else. If you ignore the other person, you're not communicating, you're pontificating.