It's part of a pay-it-forward project that started two years and 1,000 umbrellas ago and already is generating interest from around the world. (Post-Gazette.com)

If someone does you a big favour, don't pay it back... Pay It Forward*. Is it possible for one idea to change the world? Let's see... it worked in the film! (planetsicknessbag.com)

Philanthropic scholar Robert Payton explained serial reciprocity as, "the principle that says we should repay the good works done for us by the good works we, in turn, do for others" (Payton 1990, 1). Thus, in serial reciprocity, individuals "pay it forward" instead of paying it back. (learningtogive.org)