If you place an old hollow-core door out on the sidewalk, with a “Free Hollow-Core Door” sign on it, then every pedestrian that passes and reads the sign will gently knock on the door.
The Hollow-Core Door Hypothesis
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If you place an old hollow-core door out on the sidewalk, with a “Free Hollow-Core Door” sign on it, then every pedestrian that passes and reads the sign will gently knock on the door.