Only A Few Know How Much

This aphorism circulates widely under Heisenberg's name but has not been traced to a verified primary source in his writings or recorded conversations. No specific book, lecture, or letter has been identified as its origin in scholarly sources. Heisenberg expressed related ideas about intellectual humility throughout Physics and Beyond (1971) and Physics and Philosophy (1958), and the sentiment aligns with his recurrent argument that the more deeply one probes quantum theory the more one finds the limits of familiar intuition. But the specific phrasing should be treated as of uncertain attribution.