Choices and persuasion
Loss aversion
Losing something feels roughly twice as bad as gaining the same thing feels good, so people work harder to avoid losses than to win gains.
Fifty pounds lost hurts more than fifty pounds found pleases. That asymmetry makes people cautious, keeps them in arrangements they'd never choose fresh, and makes 'don't lose' messages stronger than 'gain'.
In products, people resist changes that take something away, even when they get something better. When you remove a feature, explain what replaces it and give people time.
In practice
Reminding someone that cancelling will delete their saved projects and playlists is more persuasive than listing what they'd gain by staying.
Common mistake
Guilt-tripping people out of cancelling ('No thanks, I don't want to save money'). Showing what they'll lose is fair; shaming them is a dark pattern.
Where it comes from
Part of prospect theory, set out by Daniel Kahneman and Amos Tversky in 1979. Kahneman later shared the 2002 Nobel prize in economics for this work.