Within Jewish thought, the phrase ruach shtus describes a moment when a person’s judgment becomes clouded by a temporary spirit of foolishness. Resh Lakish teaches in Sotah 3a that a person does not commit a wrongdoing unless a ruach shtus enters them. In other words, people rarely act against their values intentionally. Instead, something distorts their thinking and they temporarily behave like a fool.
Rashi explains that this spirit of folly leads a person to rationalize their actions and imagine there will be no real consequences. Building on this idea in his work the Tanya, Rabbi Shneur Zalman of Liadi teaches that every person possesses a divine soul that naturally seeks connection with G-d. Ruach shtus, however, temporarily hides this inner awareness. In that moment of spiritual forgetfulness, even a wise individual may act like a fool, convincing themselves that their actions do not truly matter.
Intelligence alone does not protect anyone from mistakes; even thoughtful people can lose perspective in moments of extreme emotion. By pausing and reflecting a person can push away the spirit of folly and return to wisdom with renewed awareness and strength.