loss-aversion

Kahneman and Tversky found that losses loom roughly twice as large as equivalent gains — losing $100 feels about as bad as gaining $200 feels good.

The evolutionary explanation: in an ancestral environment, losses are often irreversible (dead is dead), while missed gains can be recovered. Asymmetric sensitivity to loss is adaptive.

The design implication: if you want to change behavior, framing something as preventing a loss is typically more effective than framing it as achieving a gain. "Don't lose your savings" beats "grow your wealth."