Car wash customers given a 10-stamp card with two stamps already filled completed it 34% of the time. Customers given an 8-stamp card with none filled — the same eight washes — completed it 19% of the time.
We respond to the fraction of a goal already covered, not just the distance left. Framing a new initiative as “already underway” rather than “starting from zero” changes how likely people are to see it through.