What the thought is about matters far less than what happens next. Germs, illness, something too silly to say aloud: the machinery running underneath is the same in each case.

What the research says

In a brain imaging study, patients exposed to their own triggers showed habit-related circuitry taking over from the goal-directed kind, which fits the idea that a compulsion runs on ingrained urge more than on a plan to prevent something bad. If that holds, the specific fear is closer to the story told about the urge than to its cause. This was one experimental imaging study, so it supports the model rather than settling it.

Strength of evidence: one line of research. A single study, or a theoretical account.