"The blind leading the blind" is a quote from Jesus in Matthew 15 and Luke 6. In full (New American Bible) Jesus responds to a question about the Pharisees saying: "Every plant that my heavenly Father has not planted will be uprooted. Let them alone; they are blind guides (of the blind). If a blind person leads a blind person, both will fall into a pit." This echoes the words of the Katha Upanishad: "Abiding in the midst of ignorance, thinking themselves wise and learned, fools go aimlessly hither and thither, like blind led by the blind."