From Dorothy L. Sayers, Creed or Chaos? (Manchester, 1974), page 52:

“A very able surgeon put it to me like this: ‘What is happening is that nobody works for the sake of getting the thing done. The actual result of the work is a by-product; the aim of the work is to make money to do something else. Doctors practice medicine, not primarily to relieve suffering, but to make a living—the cure of the patient is something that happens on the way. Lawyers accept briefs, not because they have a passion for justice, but because the law is the profession which enables them to live. The reason why men often find themselves happy and satisfied in the army is that for the first time in their lives they find themselves doing something, not for the sake of the pay, which is miserable, but for the sake of getting the thing done.’”

HT: Ray Ortlund