Once on a university tour in Berlin, I slipped off to the bathroom. Washing my hands, I looked about for paper towels to dry them. Pasted over the dispenser was a glossy sign that read: “Most people take two towels.” I yanked out eight.

The sign was “nudge theory” 101. Popularised by books like Nudge, the aim is to get people to behave a particular way without using force or limiting choices. How? By formulating information, questions or choices in a certain way, designers can make people more likely to make a particular choice. Take organ donation. Lots of people want to donate organs, few bother to register. By making organ donation the default, few people bother to opt out and more people donate. A small change in how a decision is presented leads to a big jump in organ donations. Policymakers get the outcome they want, people remain free to say no.

But I’ve always wondered if the power of nudges would fade once people realised they were being poked in the ribs. In that bathroom in Berlin, I knew what was going on and I resented it. In that vein, here’s a scene from the Power Broker, the story of Robert Moses, describing a then-new strategy to keep a beach clean in the 1930s:

“The lines of wire trash receptacles on the clean white sand were only a symbol of the emphasis on cleanliness there also. At intervals, loudspeakers sounded a bugle call, and then an announcer, in a carefully modulated tone, “thanked” the visitors for their cooperation in keeping the beach clean. “The effect,” as one observer wrote, “is magical. In no time at all, every guilty culprit is doing KP in his immediate area.”

Being thanked for your cooperation is a rudimentary nudge. However, it’s one that usually elicits eyerolls, not “KP of the immediately area” today. So maybe nudges do wear off.