In total darkness, a fixed point of light appears to drift: it's an illusion. In 1935, Muzafer Sherif asked volunteers how far it moved. Alone, their answers varied widely; in groups, they converged on a shared norm that each person kept even when tested alone later. In 1961, an arbitrary norm planted by confederates even survived several “generations” of participants after the confederates had left.
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.