According to The Free Dictionary, the aphorism "love is blind" means that a person is unable to perceive faults in the person he loves. The phrase appears in "The Canterbury Tales," written by Geoffrey Chaucer in the late 14th century.
"Love is blind" did not enter into common usage in literature until centuries later, after it was used by William Shakespeare. Shakespeare's 1596 play "The Merchant of Venice" includes the line, "But love is blind and lovers cannot see." Current scientific research actually supports the idea that love impairs critical judgment. A 2004 study conducted by University College London found that feelings of love can actually impair parts of the brain responsible for critical thought.