He proved that treating cross-disciplinary, useless curiosity as a vocation can widen the frontier of human knowledge — but that refusing to finish and refusing to publish will bury most of a genius's output alongside him.
Born in 1452 in the town of Vinci near Florence, the illegitimate son of the notary Ser Piero and a peasant woman, Caterina. Illegitimacy barred him from university and from his father's trade as a notary — and pushed him instead into a painter's workshop. He called himself an "unlettered man" (omo sanza lettere), learning all his life from observation rather than scholastic learning. As a youth he apprenticed under the Florentine master Verrocchio. In 1482, aged 30, he wrote to sell himself to Ludovico Sforza, Duke of Milan, chiefly as a military engineer; he stayed nearly 17 years and painted The Last Supper. When Milan fell in 1500 he became a wanderer: he briefly served the warlord Cesare Borgia as a military engineer, returned to Florence, and around 1503 began the Mona Lisa. In 1516 he accepted the invitation of King Francis I of France, moved to Amboise, and died in 1519, leaving his notebooks to his pupil Melzi.
First, the job letter of 1482. At 30 he left Florence and wrote the Duke of Milan a ten-point pitch: the first nine points were all siege engines, portable bridges, and armored chariots, and only the last line added, almost in passing, "I can also paint." He judged coolly that in a violent age a man who could build weapons was more wanted than a man who could paint. It was a calculated act of self-reinvention — betting on an unproven new identity.
Second, withholding the Mona Lisa for sixteen years. The painting was commissioned around 1503 by the merchant Francesco del Giocondo and should have been delivered. Instead Leonardo kept layering veils of smoke-thin "sfumato," reworking the mouth and eyes, and never handed it over — he carried it with him from place to place until his death. He chose "endless approximation" over "delivery" — at once the height of his art and a breach of trust.
Third, crossing the Alps to France at 64 in 1516. Carrying the Mona Lisa and two other paintings, he accepted from Francis I the title of "First Painter, Engineer and Architect to the King" and a manor. In truth the king wanted not more pictures but the freedom to talk with him at will. Leonardo traded the freedom of his last years for a post where he could think in peace and never had to hand in work again.
Sources: Walter Isaacson, Leonardo da Vinci (2017), Ch. 7, 24, 33; Leonardo's letter to Sforza (c. 1482, Codex Atlanticus).In late 1499 French troops stormed Milan, the Sforza regime collapsed, and Leonardo's 17-year court career was wiped out overnight. The colossal bronze horse he had modeled for the duke — a clay original over seven meters high that had stunned the whole city — was never cast, because the bronze was seized to make cannon; French archers later used the clay model for target practice and destroyed it. Now without a stable patron, he began to drift — yet it was exactly this upheaval that forced out his most restless, most productive scientific decade: dissecting corpses, studying flowing and turbulent water, designing flying machines. In comfort he was a painter; only when displaced did he become the Leonardo we remember.
A notebook on his belt, written backwards with his left hand. He carried a small book everywhere and noted whatever he saw — about 7,200 pages survive, mostly in "mirror script" running right to left (he was left-handed). On a single page a shopping list can sit beside "why is the sky blue." He made observation as automatic as breathing.
To-do lists of pure curiosity. His notebooks list tasks with no practical aim: "Describe the tongue of the woodpecker," "Describe the jaw of the crocodile," "Ask the Fleming so-and-so how ice forms in Switzerland." These questions earned him nothing and were owed to no patron — sheer wanting to know. That "useless inquiry" was the engine of his mind.
Vegetarian, bird-freer, dressed in pink. According to his contemporary Corsali, he ate no meat, could not bear to eat animals, and often bought caged birds in the street to set them free. In an age when everyone wore dark long robes, he favored knee-length rose-pink tunics and kept his beard meticulously groomed — a man who deliberately stood apart.
A procrastinator and easily distracted — yet dissecting corpses through the night. While painting The Last Supper he would stare at the wall all day and add only a stroke or two (as the eyewitness Bandello recorded); but to understand the body he dissected some 30 corpses, drawing heart valves and a fetus in the womb by night in hospital morgues, grasping the workings of the aortic valve centuries ahead of medicine.
Sources: Isaacson (2017), Ch. 12, 27; Matteo Bandello, Novelle; Andrea Corsali's letter to Giuliano de' Medici (1515).First, chronic non-completion and repeated broken faith with patrons. The Adoration of the Magi was abandoned half-done, St Jerome left unfinished, the bronze horse never cast, The Battle of Anghiari flaked off because an experimental paint failed. Isabella d'Este, Marchioness of Mantua, chased him for a single painting for years and got nothing. The other face of genius is leaving those who trusted you empty-handed again and again.
Second, serving a butcher like Borgia. In 1502 he was hired by Cesare Borgia — the model for Machiavelli's The Prince, a warlord notorious for cruelty — touring conquered towns, drawing maps, and designing fortifications and weapons. The same man who freed caged birds in the street once coolly optimized the war machine of a killer.
Third, an output that was barely inherited. He published nothing in his lifetime; his notebooks stayed locked in private books written in near-coded mirror script. Many of his discoveries in anatomy and fluid dynamics went to the grave with him and had to be re-made by others centuries later — his science advanced no one but himself. A privately hoarded genius may contribute almost nothing, on net, to the world. (A note: in 1476 he was anonymously accused of sodomy; the case was dropped for lack of evidence, and it remains part of his contested record.)
Sources: Giorgio Vasari, Le Vite (1550/1568); Isaacson (2017), Ch. 20, 31; the correspondence of Isabella d'Este and her agents.Leonardo offers the "AI super-individual" a lesson with two faces. The upside: useless curiosity is the most underrated form of compound interest — asking about a woodpecker's tongue or why the sky is blue, questions owed to no deadline, trained the cross-domain pattern recognition that later fed his art and engineering; real breakthroughs happen at the seams between fields, not down a single specialist's shaft. The downside is a glaring warning: his science influenced almost no one, purely because he never finished and never published. For anyone chasing super-individual status this is lethal — curiosity decides how far you can go, but only delivery lets the world remember you went. AI happens to plug his weakest link: it can help you actually finish and ship the things perfectionism has stalled. Learn his curiosity — but dodge his unfinished business.