Loss aversion
Also said as Loss framing, Gain framing, Framing effect, Prospect theory
Losing something hurts more than gaining the same thing feels good. Daniel Kahneman and Amos Tversky built this into prospect theory in 1979, and in 1981 showed that wording alone can flip a choice.
It explains why players hate penalties that are mathematically the same as bonuses. Tversky and Kahneman estimated in 1992 that losses weigh roughly twice as much as gains. Gal and Rucker argued in 2018 that this is overgeneralised and depends on context. Yet a 2020 replication across 19 countries by Ruggeri and colleagues supported prospect theory's main predictions, so it stands as strong but not universal.
Say it
“Do not say "lose 20% XP if you leave the match". Say "finish the match for a 25% bonus". It's the same maths and nobody will write an angry post about it.”
Where you’ve seen it
World of Warcraft's rest system is the industry's favourite story here. Developers have described how in beta a tired character earned 50% and a rested one 100%, which players hated. It was relabelled as 100% and a 200% bonus with the same result, and players liked it. It is told as an anecdote, and the exact numbers vary between accounts.
Not to be confused with risk aversion
Risk aversion is preferring a sure thing. Loss aversion is about gains and losses feeling different, and it can make people take big risks to avoid a loss.