In 1990, researchers gave a mug to half a class, then set up a market. Owners asked roughly twice as much to sell it as others were willing to pay to buy it. As a result, hardly any trades took place. Owning something, even for a few minutes, is enough to overvalue it. It's called the endowment effect.
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.