Impact bias

The impact bias is the systematic tendency to overestimate the emotional impact of future events and to underestimate the speed of emotional adaptation. We expect that winning the lottery will make us permanently happy and that losing a job will make us permanently miserable. In reality, both effects fade far faster than we predict, because humans possess a remarkable capacity for hedonic adaptation that our forecasting machinery ignores.

The bias has been demonstrated across domains: romantic breakups, electoral outcomes, medical diagnoses, and property acquisitions. In each case, the predicted emotional intensity is higher than the experienced intensity, and the predicted duration is longer than the actual duration. The error is not random; it is structural. We simulate the future by imagining the event in isolation, but we experience the future in a context that includes compensation, reinterpretation, and the simple passage of time. The mind is a better simulator than a predictor because simulation does not require modeling the full adaptive system.