"Most guests reuse their towel" beat every environmental appeal at changing behavior

Researchers tested different hotel card messages asking guests to reuse towels. Appeals to protecting the environment barely moved behavior, but a card stating that most previous guests in that exact room had reused their towel raised reuse by roughly a third. People follow the perceived norms of people like them more readily than they follow reasoned arguments.

— Noah J. Goldstein, Robert B. Cialdini, Vladas Griskevicius, A Room with a Viewpoint: Using Social Norms to Motivate Environmental Conservation in Hotels — Journal of Consumer Research, 2008