I have been procrastinating

quite long enough. Today I must make time to start the long and painful process of writing the final draft/editing/doing something to the latest attempt. My young hero needs to come back from his "holiday" and be pulled into shape.
I am not looking forward to this. I know it will mean cutting bits of the book I like but which really do not need to be there. It will mean finding all the "typos", the apparent spelling errors, the actual spelling errors, the grammatical errors, the repetitions, the plot holes, the... well any writers reading this will know what I mean. Is the book any good at all? Will anyone actually want to read it? Why am I doing this? It is painful and deliberately putting myself in this situation makes as much sense as banging my head on the wall. It might feel good if I could stop - but I cannot stop.
Of course, as a complete masochist, I am banging the front of my head with this one and the back of my head with the one sitting patiently out there awaiting the attention of several agents. This only makes matters worse.
I sometimes wonder why I torture myself like this. What makes anyone want to write? What makes me want to write? I know about the "I like words" bit and the "I like to use my imagination" bit and the other "bits" that go into writing but none of them explain the "must".  It is almost as if the "must" is external to me. There is something out there that insists I must do this. There is some unseen law that says I have no choice.
So, today I will start - after all, I have more books I "must" write.