How it holds itself in place

Follow it round once. Notice how small the third box is, and notice which box the arrow from the last one goes back to.

The loop is not powered by the thought. It is powered by the search, and every turn makes the next arrival louder. The diagram shows a loop running through: A thought arrives, uninvited, then It means I might not believe, then Search for certainty, then Relief, about an hour, then But what if.