Why Losses Hurt More
Flip a coin: heads you win $100, tails you lose $100. The expected value is exactly zero. A rational agent should be indifferent. But almost everyone rejects this bet — because losing $100 feels about twice as bad as winning $100 feels good. This asymmetry, called loss aversion, is one of the most fundamental discoveries in behavioral economics. Daniel Kahneman and Amos Tversky documented it in their landmark 1979 paper introducing prospect theory.
The Value Function
The simulation displays prospect theory's characteristic S-shaped value function: concave above the reference point (diminishing sensitivity to gains) and convex below it (diminishing sensitivity to losses), with the loss side steeper by a factor of lambda. The default lambda of 2.25 means a $100 loss produces 2.25 times the psychological impact of a $100 gain. This simple asymmetry explains an enormous range of human behavior, from the endowment effect to the disposition effect in investing.
Animated Coin Flips
Watch the simulation run hundreds of coin flips. The running profit/loss tracker shows the random walk of cumulative outcomes. Even when the gamble has positive expected value, the psychological experience is dominated by the sharp pain of losses. The green gain bars and red loss bars are scaled by lambda, making the asymmetry visible. Notice how your gut reaction to each loss is stronger than your reaction to each gain — that is loss aversion at work, even in a simulation.
Real-World Implications
Loss aversion is not merely a laboratory curiosity. It explains why people hold losing stocks (selling would 'realize' the loss), why homeowners refuse to sell below their purchase price even in a down market, why negotiators anchor on their current position, and why the pain of a tax increase exceeds the pleasure of an equivalent tax cut. Benartzi and Thaler showed that loss aversion, combined with frequent portfolio evaluation, explains the equity premium puzzle — why stocks must offer such high returns relative to bonds. Understanding lambda is understanding why humans are not the rational agents that classical economics assumes.