Step 1: Frame the task as separating symptoms that worsen outcome from those that improve it. The established list of bad prognostic indicators in OCD includes early onset, giving in to compulsions, bizarre or hoarding compulsions, need for symmetry, comorbid depression and poor insight.
Step 2: Match the options to that list. Hoarding sits squarely among the poor prognostic features because it is treatment resistant and runs a chronic, disabling course.
Step 3: Weigh the alternatives. Cleaning driven by contamination fear tends to respond well to exposure and SSRIs, signalling a better outcome, while pathological doubt and magical thinking are typical contents of obsessions rather than validated prognostic markers.
Step 4: The choice that genuinely predicts a poor prognosis is hoarding, so the contamination-based key is corrected.
\[\boxed{\text{Hoarding}}\]