Individuals rarely achieve investment activities characterised by up-front costs and delayed benefits. Point-of-decision prompts (PDPs) provide information about a better alternative or a deterrent to the behavioural standard at the moment the decision is made and may affect behaviour by helping individuals perform this type of investment activities. We conducted a field experiment to assess the effects of a PDP intervention that encourages taking the stairs rather than the escalator in three Paris (France) Metro stations for eight weeks from April to July 2014. In total, we followed up 205 individuals and the data show that PDPs have an immediate, albeit decaying, peaked effect on individuals' stair use, with a stronger effect when weak physical effort is made salient. However, the intervention did not change individuals’ stair-use habits. In the best-case scenario, the effects last two weeks after the intervention ends. Our preferred explanation is that PDPs act as “cues” but people become accustomed to them and in the end no longer notice them. These findings suggest that a PDP intervention is not sufficient to modify individuals investment in activities with immediate costs and delayed benefits in the long-run.