From the new biography The Grand Slam: Bobby Jones, America and the Story of Golf by Mark Frost.
After Jones graduated from Georgia Tech, he decided he’d concentrate on what he felt was most important: family. Other golfers near his skill level were turning professional — teaching, playing exhibitions and participating in the professional tournaments of the time. That wasn’t what he wanted. He’d set his priorities, and they didn’t involve his sport. He did love golf, however. So he aimed to balance the two; he decided he’d play in fewer tournaments. Over the next 10 years until he retired, he played in only 40 tourneys. Of the 40, 21 were major championships — and he won 13 of them.