Hindsight bias
Etymology
From hindsight, "seeing after the event," the natural opposite of foresight. Psychologist Baruch Fischhoff gave it experimental teeth in 1975, showing that people who were told an outcome then overestimated how likely they would have judged it beforehand. The colloquial "I knew it all along" is exactly the effect it names.
noun · /HYND-syt BY-us/
The tendency, once you know how something turned out, to feel you knew it all along.
What it names
Why the past always looks more predictable than the present feels — outcomes rewrite our memory of how uncertain we actually were.
Example
After the startup collapsed, every pundit had hindsight bias — the warning signs that were invisible in 2021 were suddenly obvious.
Related idea
Confirmation bias filters new evidence to fit a belief; hindsight bias rewrites what you remember believing in the first place.