Regressive Bias
Central Tendency Bias · Contraction Bias
The tendency to remember high values and high likelihoods/probabilities/frequencies lower than they actually were and low ones higher than they actually were.
Origin
The bias takes its name from regression to the mean, a statistical phenomenon first described by Francis Galton in his 1886 study of hereditary height, published in the Journal of the Anthropological Institute. Galton found that exceptionally tall parents tended to have children closer to the average — coining the term "regression towards mediocrity." The psychological memory bias, where extreme values are recalled as less extreme, was identified later as a cognitive parallel to Galton's statistical finding.
Everyday Use
That record-hot summer day? You'll remember it as hot, but not quite as extreme as it was. That incredibly cheap deal you got? In hindsight it won't seem quite so remarkable. Our memories quietly nudge extreme experiences toward the average, making the exceptional feel more ordinary than it was.