Hindsight is 20/20 is a popular phrase, stating the fact that everyone is a wise man in hindsight.
The expression references the Snellen chart used for diagnosing eye conditions.
A 20/20 on the Snellen chart is a perfect score, used for deeming the visual acuity of someone unimpaired.
The Snellen chart, which most people recognize today as the rows of letters in varying sizes at the doctor’s office was developed by Herman Snellen in 1862.
“Hindsight is 20/20”, however, didn’t appear as a phrase until a century later, with the earliest documented cases emerging in the late 1950’s, with one of the earliest mentions appearing in a 1959 issue of The Canadian Record.
Over the years, the expression became a widespread cliché, known by most that every fool is a wise man in hindsight.
“Hindsight is 20/20” was first defined on Urban Dictionary in 2006.