That which is bred in the bone will never be out of the flesh.

A disposition or habit that has become deeply ingrained is unlikely to disappear. The bodily imagery presents a trait as something embedded throughout a person rather than a passing impulse.

The proverb expresses a strong expectation that established character will persist, even when circumstances change or someone tries to behave differently. It is a judgment about how difficult such traits are to shed, not a literal claim about the body.

Use it to comment on behavior that seems consistent with a person's long-established habits or disposition, particularly when a change of circumstances has not changed how they act. Its forceful wording can sound dismissive if applied to someone trying to change.