When you have finished a real effort of a major book [or music], you cannot start a major book the next day.  At least you cannot start more than the first few pages.  I usually make a start and then step aside and let the well fill up again.  That’s also why I move from genre to genre.  I never write two books of the same genre in a row.  I think that’s a safety valve.  If you write the same genre over and over again, you do tend to get stale.

– Madeleine L’Engle, Writers’ Workshop, Session VII, 28 January 1983