The human brain is a curious instrument. It is remarkably like the sea, possessing deeps and shallows – cold dark profundities and sunny crests. It has its breakers dashing in to shore, and its sullen backwashes. Swift currents race beneath a surface ruffled by minor winds. And there a constant pulsing rhythm in it very like the tides. For it possesses periods of ebb, when all inspiration recedes into the blind plumy distance; and periods of flow, when strong thoughts come hurtling in, resistless and supreme.
From The Chinese Orange Mystery Ellery Queen (orig. published 1934)