Why Do We Blog?

Ahh..the age old question. Be thankful I have discovered the answer! ...Ok..it's not a discovery, merely...a hypothesis.
The way I see it, GENERALLY, people blog because they may
1. Have a stand about something (religion, politics, etc)
2. Use it as a method of diarising their thoughts
3. Complain, rant, shout obscenities
4. Put up pictures for sharing
5. Have too much time on their hands

Yea...so there you have it! Could this be the first post in a blog to describe blogging? I doubt it, people in the last category may have a post like this way before mine.