Shortly after he became an officer in the Marines, John Kelly met a captain who told him that he should approach his new position as “a real professional.”

“A doctor who doesn’t read peer articles and stay attuned to the developments in his field is not the kind of doctor you would want to go to, and the same is true for officers in the Marine Corps,” the captain told him.

Kelly recounted the story in “The Leader’s Bookshelf,” a collection of essays from four-star generals about their favorite books. We first read his essay in an excerpt run by Foreign Policy.

“He got me going on reading, specifically focused on military things, and I just never stopped,” Kelly said.