The jealous are troublesome to others, but a torment to themselves.

William Penn (1644–1718), the Quaker founder of Pennsylvania, was also a prolific moral writer. The sentiment about jealousy fits the aphoristic style of his ethical reflections, which often warn against passions that disturb both social harmony and the inner life. Penn’s Quaker background emphasized inward discipline, peaceable conduct, and the spiritual costs of envy, pride, and resentment. In that milieu, jealousy was not merely a private feeling but a corrosive force that damages community relations while simultaneously punishing the person who indulges it—an idea Penn frequently expressed in compact, proverbial form in his collections of “fruits” or maxims.

Penn frames jealousy as a double harm: outwardly it makes the jealous person difficult—suspicious, accusatory, and disruptive—while inwardly it becomes self-inflicted suffering. The line suggests that jealousy is uniquely self-defeating: even when it succeeds in controlling others, it cannot bring peace to the jealous mind. Morally, the aphorism shifts attention from the jealous person’s supposed grievance to the emotion’s intrinsic pathology. The implied counsel is practical as well as ethical: to reduce conflict with others, one must address the inner passion that generates it, since jealousy punishes its host more reliably than it protects them.