As the PGA Championship draws a collection of club professionals who join the big leagues for this one week, we examine the myriad elements that separate players at the height of the sport from those just one tier down. Whether it’s physical, psychological, or a simple matter of luck, we look at why a journeyman pro named Bob May could take Tiger Woods to a playoff 20 years ago in the PGA and not keep his tour card soon after; or why certain players with plenty of talent can hang with the best in a friendly game, only to struggle once the competition begins for real.