The phrase is a metaphor used to describe a situation when uninformed people are being advised or led by others who appear to be inept. Usually, it carries a connotation of harm and misfortune inflicted on the inexperienced by their misguided superiors. Although the saying was widely used in antiquity, it does not conform to modern understandings of the ability of blind persons to carry out full and enriching lives or to guide, lead, and teach others who are blind or sighted.
The expression appears already in the Upanishads (800–200 B.C.E.), the sacred Hindu treatises, where we read, “Fools go aimlessly hither and thither, like blind led by the blind” (Katha U. 2:5). In the Mediterranean world, the expression is first attested in the first century B.C.E., with the Roman lyric poet Horace, who in a literary letter to his friend Scaeva (Epistles 1.17.3–4) says of himself: ut si caecus iter monstrare velit (“as if a blind man sought to show the way”).
These early variations on the phrase notwithstanding, the common understanding of the idiom owes to the biblical parable of the blind leading the blind. The parable is recorded in the Gospel of Matthew 15:14, where it is used by Jesus when talking to his disciples about the Pharisees as incompetent leaders of the people: “Let them alone; they are blind guides of the blind. And if one blind person guides another, both will fall into a pit.”