What is the origin of the idiom "the blind leading the blind" and when to use it?

The idiom "the blind leading the blind" has its origins in the Bible, specifically in the Gospel of Matthew (Matthew 15:14): "Let them alone; they are blind guides of the blind. And if a blind man guides a blind man, both will fall into a pit." This biblical metaphor reflects the idea of someone who lacks knowledge or understanding trying to lead or guide others who are equally lacking in those qualities. This expression is used to describe a situation in which an uninformed or inexperienced person is attempting to guide or advise others who are similarly uninformed or inexperienced. It implies that none of them possess the necessary knowledge or expertise, and the outcome is likely to be disastrous or ineffective.