I recently posted on how public park builder, Robert Moses, used the psychology of sunk costs to get more money for his ambitious projects. Once those projects were complete, he also used social psychology to keep them clean. It had to do with the directions he gave to the people hired to clean up the Parks:
Patrolling the Boardwalk, conspicuous in snow-white sailor suits and caps, they hurried to pick up dropped papers and cigarette butts while the droppers were still in the vicinity. They never reprimanded the culprits, but simply bent down, picked up the litter, and put it in a trash basket. To make the resultant embarrassment of the litterers more acute, Moses refused to let the Courtesy Squatters use sharp-pointed sticks to pick up litter without stooping. He wanted the earnest, clean-cut college boys stooping, Moses explained to his aides. It would make the litterers more ashamed.
Once again, he displayed how a brilliant understanding of human nature comes in handy, when you are trying to influence people.