Even if Newton started thinking about gravity in 1666, it took him years of painstaking work before he understood it. He filled entire vellum notebooks with his scribbles and spent weeks recording the exact movements of a pendulum. (It made, on average, 1,512 ticks per hour.) The discovery of gravity, in other words, wasn’t a flash of insight - it required decades of effort, which is one of the reasons Newton didn’t publish his theory until 1687, in the “Principia.”

Although biographers have long celebrated Newton’s intellect - he also pioneered calculus - it’s clear that his achievements aren’t solely a byproduct of his piercing intelligence. Newton also had an astonishing ability to persist in the face of obstacles, to stick with the same stubborn mystery - why did the apple fall, but the moon remain in the sky? - until he found the answer.