A driver is moving through fog and can see only the nearest meter of road. A map becomes useless at every turn, because there are no landmarks in sight. Maxwell's demon, which tries to extract work from thermal motion, finds itself in a similar situation when its measurements are noisy. Researchers have shown that in such fog, a simple glance at the present moment is more reliable than a detailed memory of the journey.

In the experiment, a tiny plate oscillates at a frequency of 1100 Hz, and its position is measured to within 1 pm, but noise is added, like grime on the windshield. A control force switches depending on the sign of the measured coordinate, and a little work is extracted from the thermal fluctuations. The more precisely the demon knows where the plate is, the more work it extracts.

When the measurements are nearly perfect, the bound that remembers everything turns out to be the best. But add noise, and that bound quickly weakens. The simple instantaneous relationship holds up better and accurately predicts how much work can be extracted. The fog thickens, and the driver stops looking at the map, watching only what is visible right in front of the hood.