why a blog?

A co-worker of mine said he didn't get what a blog is about? I didn't tell him I blog occasionally. I said I thought it was like a journal...then I thought why do I have a blog? No one reads it, and do I really care? So I was thinking why do it? It is for people who are full of hot air and want to be heard? The people in my life probably already know everything I would write about. Do bloggers feel a need to say to the world look at me and what I wrote. It's more important than anything you'll ever have to say. I'm full of myself.
So, calling all bloggers....what is the point...exactly?