Franklin warns against attacking or criticising others when one is vulnerable to the same kind of judgement. The image is practical: someone who throws stones at a neighbour while living behind glass windows risks having the stones returned and suffering greater damage themselves.

The saying therefore concerns both hypocrisy and prudence. Before condemning another person’s faults, it is sensible to consider whether similar weaknesses exist in one’s own conduct. Criticism can lose credibility when the critic is guilty of comparable behaviour, and hostility can invite retaliation. Franklin’s point is not that people must be flawless before raising legitimate concerns, but that judgement should be accompanied by self-awareness and restraint. The broader lesson is to examine one’s own vulnerabilities before exposing those of others, particularly when criticism is harsh, personal or likely to provoke a response.