Loss aversion is a behavioral bias capturing the notion that people tend to prefer avoiding losses over acquiring equivalent gains. In economics, this bias is illustrated in theoretical, experimental and empirical work.

The concept of loss aversion was introduced by Kahneman and Tversky and is an important part of prospect theory. Since then theoretical work has advanced in various directions, such as expectation-based loss aversion by Kőszegi and Rabin. In experimental work, the endowment effect is commonly seen as a manifestation of loss aversion.

See more: https://en.wikipedia.org/wiki/Loss_aversion