The understanding you have of events only after they've happened; seeing things clearly in the past when you couldn't before.
Compound of 'hind' (rear, back, from Old English) and 'sight' (vision). Originally a shooting term meaning the rear sight on a gun; metaphorically extended to past understanding.
Hindsight is called '20/20' because perfect vision is 20/20—but we only achieve this perfect vision backwards in time, never about what's coming.
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