evidence: There’s no question that Renaissance polymath Leonardo da Vinci was brilliant, but he only finished a fraction of the projects he started. Sam Kean argues that the problem was his inability to focus—his own intelligence kept getting in the way. [...] In the early 1500s, Leonardo da Vinci was chatting with friends in a piazza in Florence. They were discussing Dante’s Divine Comedy. Someone asked Leonardo his opinion about one passage. And Leonardo began stroking his long red beard. He was stumped. [...] In 1483, when Leonardo was thirty-one, he applied for a patronage with the Duke of Milan. And his application letter is completely over the top. In it, Leonardo bragged about his expertise with an absurd number of technologies—bridges, dikes, ships, catapults, cannons, canals, covered wagons, and more. He also claimed to sing like a nightingale—and, oh, was the best artist in Europe.