This is an excerpt from I Will Lead You Along: The Life of Henry B. Eyring by, Robert I. Eaton and Henry J. Eyring.
Hal often sought his father’s assistance with difficult physics problems. Henry was a master mathematician, capable of solving complex equations in his head. The window of time to get his help, though, was narrow. Henry invariably stayed at the university until dinnertime, six o’clock. And Hal had a time constraint on the back end—his goal was to have the physics homework done before pickup basketball games at the university started at seven. To hit this narrow window, he tried to solve all but the knottiest problems in the late afternoon, leaving only a few to take to his father after they had finished dinner.
The strategy would have worked well were it not for Henry’s belief in the importance of understanding what he called the “first principles” of physics. When Hal asked for help with a particularly complex equation, one needed to solve an unworked homework problem, his father typically replied, “Hal, let’s not worry about what the textbook says; we can derive this equation ourselves, from first principles.”
That would lead to a time-consuming trip downstairs, where a chalkboard hung on an unfinished basement wall. There Henry would begin to write the most fundamental equations of physics. From these he would lead Hal through an exercise of deriving for himself the complex formulae in his textbook. Working from first principles was, Henry knew, the best way to teach Hal not only physics but also the broader life lesson of paying the price to really understand a problem before trying to solve it. His willingness to spend time with Hal in front of the chalkboard reflected his belief that Hal had the capacity to be a good problem solver.
The rub, though, was that this deep dive into mathematical fundamentals nearly always took longer than Hal hoped, making him late for basketball games that were already under way by the time he arrived. It was at one of these tense moments, with precious court time slipping away, that Henry suddenly stopped. “Hal,” he said, “we did this same kind of problem a week ago. You don’t seem to know it any better now than you did then. Haven’t you been working on it?” Embarrassed, Hal admitted that he hadn’t been studying the problem.
Henry stepped back from the board and looked into his son’s eyes. “You don’t understand, Hal,” he said. “When you walk down the street, when you’re in the shower, when you don’t have to be thinking about anything else, isn’t this what you think about?” Again, the answer was no. It was a poignant moment for Henry, who had hoped that all of his sons would become scientists. After a pause, he said, “Hal, I think you’d better get out of physics. You ought to find something you love so much that when you don’t have to think about anything, that’s what you think about.”
(Robert I. Eaton and Henry J. Eyring, I Will Lead You Along: The Life of Henry B. Eyring [Salt Lake City: Deseret Book, 2013], 48–50).