Hindsight bias
Also known as: Knew-it-all-along effect
Once we know how it turned out, we feel we saw it coming all along.
What it means
Hindsight bias is the tendency, once an outcome is known, to overestimate how predictable it was beforehand and to misremember one's own earlier expectations as closer to what actually happened. The mechanism is reconstructive: learning the outcome makes the path to it feel inevitable, so the mind updates the memory of the prior belief to fit the present knowledge, a process tightly linked to the difficulty of un-knowing what you now know. Three components are usually distinguished — memory distortion ('I said it would happen'), inevitability ('it had to happen'), and foreseeability ('I knew it would happen') — and they can arise from different causes. The bias corrupts learning from experience, because outcomes that felt genuinely uncertain in advance are recoded as obvious, robbing the decision of its real difficulty. In practice it fuels unfair blame: investigators, juries, and managers judge decision-makers as negligent for not foreseeing risks that were, at the time, only one of many plausible futures.
Examples
After an election, pundits call the result 'obvious in retrospect' — though the same commentators forecast the opposite the week before and have simply forgotten doing so.
After a startup collapses, every board member recalls spotting the warning signs early — yet the minutes from a year before record their unanimous, untroubled approval of the same strategy.
A jury that knows the flood happened finds the council negligent for skipping the barrier, though at the time that risk was one of a dozen competing for the same budget.
First described in Baruch Fischhoff (1975).