Tiger Woods has it, Ben Hogan had it, and both attained legendary status with it.
In simple terms, it is the ability to overcome pain regardless of the circumstances.
Tiger's achievement at Torrey Pines will go down as absolutely superb, considering he had not played 18 holes since competing in The Masters last April.
Some doubts are being expressed about the great man competing at Royal Birkdale next month in the British Open—however, it would be a brave man who would wager against this happening.
Tiger Woods is simply a phenomenon.
He is a true successor to another great American golfer, who also became a legend during his lifetime.
Ben Hogan, the Texan, stunned the world by emerging victorious in the US Open 16 months after suffering horrific injuries in a car crash.
Hogan was travelling away from a tournament in Phoenix to return to his home in Fort Worth when through the morning fog, a Greyhound bus smashed into the side of his car and Hogan's first action was to throw him self across the lap of his wife, Valerie, taking the full brunt of the collision and, it is generally accepted, saving her life.
Hogan sustained a double fracture of the pelvis, a broken collar bone, broken ribs, a mangled ankle, a ruptured bladder, a blood clot to the right lung, plus multiple cuts and bruises.
The following day, the Associated Press issued his obituary to newspapers throughout the land.
Surgeons predicted Hogan would never walk again.
11 months after the accident, with his legs freshly bandaged every day, the Texan lost in a play-off to Sam Snead for the Los Angeles Open.
In 1950 he won the US Open by finishing four shots ahead of Lloyd Mangrum in another play-off.
In 1951 he had his name again on the US Open trophy, two years later repeating the feat and with it the Masters, plus the British Open at Carnoustie, where the Scots awarded him with the accolade of "The Wee Ice Mon"
Hogan and Woods have something many would give their eye teeth to obtain.