"Blind Leading the Blind"

"It's like the blind leading the blind..." is a rather un-PC comment about receiving guidance that is less expert than you were hoping for. Like the teacher who can't spell. Or the parachute course instructor who suffers from vertigo.

Jesus made this saying famous when he rather bitingly attacked the Pharisees, a religious group of his time which Jesus characterised as keeping the letter of the law, but not its spirit...
Stay away from those Pharisees! They are like blind people leading other blind people, and all of them will fall into a ditch."

Matthew 15:14