Absolutely true story: A friend of mine could make a golf ball do just about anything and was a wonder to watch. He was a scratch player or better (I don't recall his exact handicap). On paper, he was professional standard. He could sink 10 foot putts all day long (my hyperbole), but what he could not do was sink a 10-foot putt, when it counted. By his own admission, he just did not have the match temperament to perform when the pressure was really on.
Golf at professional level is not just about skill, but also mental preparedness, fitness and probably a lot of other factors.
I've played my entire life, and run a handful of people with the exact same game.
Nick Faldo did an interview with Joe Buck where they touched on the subject, and he said without the complete conviction that you're going to sink the putt/make the birdie/win the tournament - you'll never accomplish any of it.
At the Pro level, the mental aspect of the game is more important than the physical.
While this is true, I think golf etiquette makes it easier to handle the mental side. No screaming fans and flashing lights to deal with during the game like in other sports.
Also, depending on how you handle pressure, a period of absolute silence when people concentrate on seeing whether you fail or not can be a lot more nerve-wracking than a colourful crowd of people relentlessly booing your team.
Golf at professional level is not just about skill, but also mental preparedness, fitness and probably a lot of other factors.