Let not the cobbler go beyond his last.

The cobbler’s last is a tool used in making shoes. The image urges a craftsperson to keep judgments within the bounds of the work they know well.

More broadly, the proverb warns against speaking with authority on matters outside one’s competence. It questions overconfidence, not the value of learning something new.

Use it to caution someone who offers a confident judgment in a field they do not understand well. It can sound dismissive when directed at a person rather than their particular claim.