In 1969, Stanley Milgram placed confederates on a New York sidewalk, staring up at a sixth-floor window where nothing was happening. With a single confederate, 42% of passersby looked up too. With fifteen, 86% did, and 40% stopped in their tracks to stare. The bigger the crowd, the stronger the pull: we treat other people's attention as valuable information.
Remembering is not replaying a recording — it is rebuilding. Each time you recall a memory, it becomes temporarily malleable and can be altered before being stored again. That is why two people can sincerely remember the same event… differently.
In 2003, Johnson and Goldstein compared European countries. Where you must tick a box to become a donor, consent rates ranged from 4% to 28%. Where you're a donor by default unless you opt out, they topped 85%. People aren't more generous on one side; most simply stick with whatever option was chosen for them.