It is often referred to as the most important distance in golf; the five inches between the ears.
The game is as much a test of temperament as technique and champions at the very highest level have to conquer both elements to land the biggest titles.
In their pomp the likes of Colin Montgomerie and Lee Westwood had the physical attributes to win any tournament they played. But something would always get in the way when it came to the majors; the big four tournaments that define careers.
There was always a stumbling block at the Masters, The Open, the US Open or US PGA Championship. It prevented them, and many others, from producing their best shots when they most needed them.
It is not a slight to say this. It's golf. The mental challenge of pulling off key shots when the only inhibiter is the pressure of the moment encapsulates the magic of the game.
It will be evident in abundance again this week as Rory McIlroy embarks on his latest attempt to complete the career Grand Slam. He is among the world's best who are all gathering together for the first time in eight months for the Masters at Augusta National.
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'McIlroy's biggest challenge is mental'
These major weeks are the ultimate individual examination and for all his prolific form at tour level, McIlroy has failed to add to his tally of four major wins since 2014.
We wonder why Westwood and Monty never won a major, why it took Phil Mickelson until his 13th year on tour to land his first win on this elevated stage but the most burning current question surrounds McIlroy's frustrations - the majors and most pertinently the Masters.
So precocious was the Northern Irishman's talent when he first competed as a teenager in 2009 he was asked about completing the Grand Slam by the age of 22.
Two years on at Augusta he led by four shots going into the final round, only to shoot 80 in a scarring denouement. Despite four subsequent top-five finishes, he has never since embarked on the final day back nine with a real chance of glory.
"The biggest challenge for Rory is the mental one," said Paul McGinley. The former Ryder Cup captain's Golf Channel colleague, Brandel Chamblee, added of the Masters. "It is literally his nemesis, It brings out the worst golf in Rory annually."
'It's like a mini form of PTSD'
