There are people who think that everything one does with a serious face is sensible.

Georg Christoph Lichtenberg (1742–1799), a German physicist and one of the Enlightenment’s sharpest satirists, is best known for his posthumously published notebooks (the “Sudelbücher,” or waste books). In these aphoristic jottings he skewers social pretension, false learning, and the ways people mistake appearances for substance. The remark fits his recurring interest in the theater of respectability—how tone, posture, and facial expression can substitute for evidence or clear thinking. It likely originated as a notebook entry rather than a public speech, reflecting his habit of capturing quick observations about everyday judgment and self-deception.

Lichtenberg is mocking a common cognitive shortcut: equating seriousness of demeanor with seriousness of thought. A “serious face” becomes a social credential, allowing empty, foolish, or even harmful actions to pass as “sensible” simply because they are performed solemnly. The aphorism targets both the performer (who may exploit gravitas as a disguise) and the audience (who may be too deferential to question what looks earnest). In Enlightenment terms, it is a plea for critical scrutiny over surface impressions—judging ideas by reasons and results, not by the authority-signals of solemnity.