Franklin suggests that harmful habits and poor advice can leave a lasting mark. Once a bad custom becomes familiar, repetition may make it difficult to change. In the same way, misguided advice can continue to influence judgement even after a person has reason to question it. What is learned or practised repeatedly is not always easily discarded.

The saying therefore draws attention to the persistence of negative influences. It does not mean that bad habits or mistaken ideas can never be corrected, but that prevention may be easier than unlearning them later. Franklin’s broader lesson is to be selective about the behaviours one adopts and the guidance one accepts. Early habits, repeated practices and trusted advice can shape later choices, so their quality matters precisely because their effects may continue long after they were first acquired.