The Greatest Deception Men Suffer Is

This maxim appears in Leonardo's notebooks and reflects a recurring theme in his writing: the danger of comforting illusions and received wisdom. Da Vinci was largely self-taught, having had little formal schooling, and he positioned his own method of direct observation against the opinion-based learning prevalent in Renaissance scholarly culture. His notebooks are filled with challenges to received authority — in medicine, in Ptolemaic astronomy, and in Aristotelian physics — driven by firsthand experiment and observation.