From Graham Wallas, The Art of Thought:

Voluntary abstention from conscious thought on any particular problem may, itself, take two forms: the period of abstention may be spent either in conscious mental work on other problems, or in a relaxation from all conscious mental / work. The first kind of incubation economizes Time, and is therefore often the better. We can often get more result in the same time by beginning several problems in succession, and voluntarily leaving them unfinished while we turn to others, than by finishing our work on each problem at one sitting. A well-known academic psychologist, for instance, who was also a preacher, told me that he found by experience that his Sunday sermon was much better if he posed the problem on Monday, than if he did so later in the week, although he might give the same number of hours of conscious work to it in each case.

But, in the case of the more difficult forms of creative thought, the making, for instance, of a scientific discovery, or the writing of a poem or play or the formulation of an important political decision, it is desirable not only that there should be an interval free from conscious thought on the particular problem concerned, but also that that interval should be so spent that nothing should interfere with the free working of the unconscious or partially conscious processes of the mind. In those cases, the stage of incubation should include a large amount of actual mental relaxation. It would, indeed, be interesting to examine from that point of view, the biographies of a couple of hundred original thinkers and writers.

It would, Wallas. You’re absolutely right.

Basically, this is a big part of my book.