He who slings mud generally loses ground.

Stevenson’s aphorism warns that negative campaigning and personal attacks are self-defeating. The image is physical: if you stop to throw mud, you literally lose footing and traction—suggesting that character assassination costs the attacker momentum, credibility, and moral standing. In politics, “mud” implies insinuation, gossip, and distortion; the line argues that such tactics may briefly soil an opponent but ultimately damage the slinger more, by revealing pettiness and distracting from substantive issues. The proverb-like phrasing also implies a general ethical principle beyond elections: people who try to elevate themselves by degrading others often end up diminished.