Why do we blog?

Why do we write diaries and blogs?
Because our lives are exciting to other people? To share thoughts? To indulge in our own personality and ideas? Because otherwise we won't remember the day? To leave something behind when we leave this universe?
I have a pretty damn boring life. For thoughts, indulgence and ideas I write stories. Remembering pointless things from the day means nothing to me.
For me, the only thing I'd ever blog or write a diary for is a sense of impending death. Or an assingment, of course.
In my writing class, I don't just write for the assingments, I write also for myself. It is an enjoyable thing I'd love to do as a job.
Is there anyone out there who does it for any other reason? I think most of the people reading this from UC's Networked Media Production class will feel their only reason is as an assingment.
Go on, tell me.