Source: Prospect Theory: An Analysis of Decision under Risk (1979), by Daniel Kahneman and Amos Tversky

Prospect theory describes the way people choose between probabilistic alternatives that involve risk, where the probabilities of outcomes are known. The theory states that people make decisions using a set of predictable rules, and these rules often run contrary to the rule of maximizing one’s net worth. It’s not a stretch to say that "Prospect Theory" is the most cited and influential academic paper of the last 50 years.