He is no wise man who will quit a certainty for an uncertainty.

The aphorism warns against abandoning a known, dependable good for a speculative alternative. It reflects a conservative strain in Johnson’s moral thinking: prudence is a virtue, and rational choice should weigh real, present advantages more heavily than imagined gains. The line also implies an ethical dimension—wisdom consists not merely in daring or ambition, but in disciplined judgment about risk, stability, and the limits of foresight. In modern terms, it cautions against “grass is greener” thinking, urging skepticism toward novelty when it requires sacrificing what is already secure.