The vanity of it all

So, I use the internet every day - I NEED to check Facebook every day and feel cut off from the world when I don't have access to my comfort blanket.
I have been toying with the idea of writing a blog for months if not years. The question is, is it a modern way of keeping a diary or is it pure vanity and that you think other people would want to read your random musings......
Which reminds me of Twitter. What is the point of it ? As far as I can work out, and I speak from a not very sound knowledge base seeing that I have never even looked at Twitter, it's all about gaining as many followers as possible and then publishing all the mundane and not so mundane details of your life.
Which is fine, but why do we think others would want to know ?
How do celebs even find the time to publish things, and why do they, seeing they are always complaining about having their privacy invaded ? The conclusion I have reached, is that it's all just one big ego thing. People follow me, read what I am up to and may even tweet back - hence I must be interesting and well liked. It's just a thought, and I am happy for people to point out the flaws in this argument.
In fact, some might argue that what I am doing here, is expecting people to read my thoughts, hence thinking I am more interesting than I actually am, in short this is all about my vanity ! I'll just have to keep on writing and see what develops.