Geoff Dyer: “Have more than one idea on the go at any one time. If it’s a choice between writing a book and doing nothing I will always choose the latter. It’s only if I have an idea for two books that I choose one rather than the other. I always have to feel that I’m bunking off from something.”
The military has a saying that “two is one and one is none.” The author quoted above gives a good explanation for why this is true for authors.
NOTE: bunking off is apparently a Britishism for goofing off.
The quote came from a post, “10 Rules for Writing Fiction,” in the Guardian in the UK.