Those lacking the skills or knowledge for something are being guided by equally inept individuals. For example, Bill's teaching his son carpentry; that's a case of the blind leading the blind. The expression is found in the New Testament as one of Jesus's teachings (Matthew 15:14; Luke 6:39). [c. 1600]

An expression applied to leaders who know as little as their followers and are therefore likely to lead them astray: “When it comes to science and technology, many politicians know as little as the average citizen; they're the blind leading the blind.”