A pay-it-forward scheme works like this. Person A does a good deed for Person B and just asks that, in return, Person B does a good deed for someone. Person B does a good deed for Person C and just asks that, in return, Person C does a good deed for someone. The cycle continues like this, with the goal being to create a flowing river of good deeds.
Pay-it-forward schemes have been a trope for a very, very long time, there was even a bad movie made about it (oh Hollywood, what would we do without you). However, as even the movie acknowledges, they are notorious for eventually fizzling out. If you had the authority or whatever that would allow you to and were to ignite a chain for as long as possible, how would you do it?
This reminds me of when i read about ancient norse gift giving culture years ago. Apparently it was expected that when you had a relationship like say a friend youd give them a gift, and youd get a gift back that was a little better usually. But it was considered really rude to give someone a huge gift that would be a burden for them to gift you something similar in return. Since the expectation was theyd give an equal or better gift back, and your placing this huge social burden on them to come up with something appropriate.