A fair face may hide a foul heart.

Understand the thought

Meaning in plain English

An attractive appearance does not establish good intentions or conduct. Judge the relevant behaviour rather than assuming that someone is trustworthy because they look appealing.

What the words are saying

The fair face supplies a pleasing outward impression, while the foul heart represents intentions or character that the appearance does not disclose. May is important: the proverb allows for a mismatch without saying that attractive people are especially dishonest. It warns about the inference from looks to goodness, not about beauty itself. An appearance can be genuine without answering a question about reliability. The useful response looks for relevant conduct, consistency and clear arrangements before making a judgement. Reversing the prejudice would be equally mistaken: an unappealing impression is not evidence of bad character either, and suspicion still needs a concrete basis.

Everyday example

A club member checks how a prospective organiser has handled shared responsibilities instead of taking a polished photograph as proof of reliability.

When to use it

Use it when attractiveness is being mistaken for evidence of trustworthy conduct.

Agent-assisted editorial interpretation. This explains the words; it does not by itself verify their author or earliest origin.