Explain why each intruding idea in desultory thinking is described as being, in itself, a "simple and reasonable thought."

What makes desultory thinking distinctive is that the disturbance lies entirely in timing and continuity, not in the content or coherence of any single idea. Each intruding thought would be a perfectly ordinary, sensible contribution if it had occurred at the right moment in the conversation; the problem is only that it forces its way in at the wrong point, disrupting the flow of an otherwise intact and purposeful train of thought. This matters clinically because it distinguishes desultory thinking from patterns in which the ideas themselves are bizarre, fragmented, or nonsensical: here, a clinician listening carefully can recognise that the person's underlying thinking apparatus for generating coherent, reasonable ideas remains largely intact, and that the deficit lies specifically in the mechanism that keeps a train of thought running smoothly from one idea to the next.