Why?

When I get a great writing idea, I think about it for about two seconds, then deliberately go and do something else. Watch some TV maybe or eat some cake. Basically, making a conscious effort to avoid it. Why? Surely I should immediately develop that idea, burning as it is in the embers of creation? It's the same with the actual writing. If I'm on a roll and I write a great sentence, I just stop and go and play some Fifa 08, stuffing my face with chocolate between passes. Why don't I go for the next sentence? Why do I feel the need to reward myself and pack up shop? Why why why why why?

Actually, I think I know. It's one of these two:

a. The idea is a newborn baby. You should wrap it up and put it in a cot and leave it for a bit. Same with the great sentence - that's you stretching to the limits of your abilities. Push any more and you'll pull a muscle. In your brain. Nasty.

b. I am a bone-idle bastard.