blind leading the blind, the

Those who try to teach or guide others, even though they know no more than their pupils. The phrase comes from the Bible, presented as one of Jesus’s teachings in the books of Matthew (15:14) and Luke (6:39). It is quoted by numerous writers thereafter and is a proverb in John Heywood’s collection in 1546: “Where the blynd leadth the blynd, both fall in the dike.”