Motivation and habit
Endowment effect
People value something more once they feel it's theirs, even if they've only had it for a few minutes.
Ownership changes how much people want to keep something. In experiments, people given a mug asked for about twice as much to sell it as others would pay to buy the same mug.
In products, ownership can come before payment: a trial with the person's own data in it, a customised setup, a saved playlist. Once it's theirs, losing it feels like a loss rather than a missed gain.
In practice
A free trial that has people import their own projects tends to be cancelled less often than one that shows a demo workspace, because the work inside is theirs.
Common mistake
Holding people's things hostage, such as making it hard to export their data when they leave. It turns goodwill into resentment, and in some places breaks the law.
Where it comes from
Richard Thaler named it in 1980. Daniel Kahneman, Jack Knetsch and Thaler's coffee mug experiments, published in 1990, are the best-known evidence.