hindsight (n.) Look up hindsight at Dictionary.com
by 1841, "backsight of a firearm," from hind (adj.) + sight. Meaning "seeing what has happened" is attested by 1862, American English, (in proverbial "If our foresight was as good as our hindsight, it would be an easy matter to get rich"), probably a formation on the model of foresight.