The PGA Championship might be the hardest to win of the four majors, even if it seems to play the easiest.
Tiger Woods and Vijay Singh are the only multiple winners of the PGA Championship over the last 15 years, a testament to a major where every player - except for the 20 club pros - believe they have a realistic chance of hoisting the Wanamaker Trophy.
Since the world ranking began in 1986, no other major has produced more champions outside the top 100 - John Daly, Shaun Micheel, Y.E. Yang and Keegan Bradley.
What makes it hard to win is the strength of the field. Everyone from the top 108 in the world ranking was scheduled to play at Valhalla Golf Club in Louisville, Kentucky. Even with Dustin Johnson (No. 16) taking a leave of absence, no other tournament is loaded with so many great players.
That's what led Ernie Els to describe the field as a "PGA Tour event on steroids."
So why are the scores so low?
Being played in the heat of the summer means more thunderstorms, or temperatures so hot that officials have to put more water on the course to keep the grass alive. Either way, it often leads to softer conditions and better scores.
The lowest 72-hole score in any major was posted by David Toms when he won the PGA in 2001 at Atlanta Athletic Club.
Of the 26 times that players have shot all four rounds in the 60s at a major, 16 have been at the PGA Championship.
"How can I bloody put this?" Els said, searching for the right words to explain what makes the final major different from the other three. "When I get on the first tee at the PGA, I'm not as nervous as when I get on the first tee at the Masters, or the U.S. Open or The Open Championship. I think with the golf course in mind, mentally you know you can score. You can go on scoring runs. The other majors, you're trying to place yourself. You're trying to see where your game is or see what the golf course is taking.
"At the PGA, you've got to have an aggressive mindset," he said. "And with the players that strong in the field, you know you have to go low."
The question is how this bodes for someone like Woods, who is trying to salvage a lost season, and for Rory McIlroy, who is on the verge of a special season.
In soft, benign conditions at Congressional three years ago, McIlroy set the 72-hole scoring record at the U.S. Open and won by eight shots. In moderate wind and slightly soft conditions at Royal Liverpool last month, McIlroy went wire-to-wire for a comfortable victory in the British Open.
"I feel like I've got a lot of momentum," he said. "And I can carry that through to the end of the year, and hopefully ride that and play some really good golf, and some golf similar to what you saw at Hoylake."
Only six players - including Woods twice - have won the final two majors of the year.
Woods would settle for any major at this point. It's tough enough that he has been stuck on 14 majors since winning the 2008 U.S. Open. These days, it's a chore just to play in them. He had back surgery on March 31, forcing him to miss the Masters and the U.S. Open.
Woods won the British Open the last time it was held at Royal Liverpool. This year, he finished 69th. Now he goes back to Valhalla, where he won the PGA Championship in 2000 at the height of his game. Woods made a 6-foot birdie putt on the final hole to force a playoff with Bob May, a putt that Woods still considers the biggest of his career. They finished at 18-under 270, the lowest score to par in PGA history.
Woods won the playoff and went on to complete his unprecedented sweep of the majors.
"It's not too often where you're tied for the lead at a major championship and you go out and shoot 31 on the back nine and lose," Woods said. "Unfortunately for Bob, that's what happened."
That it was May who challenged Woods that day speaks to how wide open the PGA Championship can be. May never won a PGA Tour event and was No. 111 in the world that week.
Those moments are becoming rare, however. It has been three years since anyone outside the top 40 won a major.
The five years after Woods won his last major created equal opportunity. There were 15 first-time champions in a span of 19 majors. Now, some of those first-timers are becoming multiple major champions.
For the first time since 1983, three players who previously won majors have captured the first three of the year. Bubba Watson won his second green jacket. Martin Kaymer added his second major at the U.S. Open. McIlroy picked up the third leg of the Grand Slam at the British Open.
"There are these first-time winners, some new faces, guys winning their first major," Adam Scott said. "And now guys are winning their second or third major, establishing the greatest players of this era of the game now. That's probably what we're seeing. And over the next few years, if they don't add more or some other guys win more, we'll be looking back and talking about Bubba and Martin and Rory in the future, much like we spoke of Ernie, Phil (Mickelson) and Tiger and Vijay."
"There weren't that many guys out here with multiple majors for a while," he said. "I think we're getting to another level of the game now where we're seeing the new era of great players."
Who's next? At the PGA Championship, history shows it could be just about anyone.