Nobody knows exactly what to expect today in round one of the WGC-Bridgestone Invitational, least of all Rory McIlroy or Harry Diamond.
The two lifelong friends from Northern Ireland will go to the 10th tee for their 8.10am (1.10pm UK time) start time, and will receive a friendly greeting from Jordan Spieth and his caddie Michael Greller, and Jason Day and his caddie, Colin Swatton.
After that, it’s down to business in one of the biggest tournaments outside of a Major, and it’s a serious undertaking.
Just 76 starters, four rounds guaranteed, $9.75m (£7.3m) in prize money with $1.66m (£1.25m) for the winner, and world ranking and FedEx Cup points available.
What to make of it all? First, the positives. McIlroy ended a naggingly persistent sense of unease and staleness that had grown within his part of the relationship with caddie JP Fitzgerald by calling it a day.
He did so knowing it would cause a major furore outside his camp, and also that, for a time at least, their friendship would most likely take on a coolness that will probably take some time to heal.
But McIlroy had the guts to do what he feels is best for his career with time running out in an injury-disrupted season. The head ruled the heart. It’s business, not personal.
He rightly said there is no good time to part company with someone who had been at his side through their march to massive worldwide success, including four Majors.
Second, McIlroy avoids a degree of stress in trying to arrange a permanent replacement at short notice by having his best pal, and best man at his recent wedding, Diamond, on the bag for the Bridgestone and the US PGA next week.
Inside the ropes, he knows he has a wingman with whom he can relax and feel comfortable.
Diamond, 31, has done some caddying for Rory in the past. He has also been part of his friend’s entourage in Majors and knows how McIlroy felt in the good and bad times.
This is a different situation. Diamond will be front and centre in the arena, and will not have experienced the level of intensity and concentration required for this tournament.
He faces a degree of pressure, but on the plus side, Diamond knows golf extremely well.
He is a former Irish Youths and senior international who has won the West of Ireland title and reached the North of Ireland championship final in the amateur ranks.
He comes from a well-off family and has business interests in Northern Ireland.
I first met him in 2004 when I accompanied the Irish Youths panel to a training week in La Cala Resort, near Malaga. Diamond impressed me with his golf, but also his confidence and his pleasant demeanour.
Eight years later, I covered the West of Ireland championship which Diamond won, to join McIlroy on the list of winners.
His personal and golfing background means the caddie should not be unduly fazed by his surroundings.
For McIlroy, in the short-term, the novelty of having Diamond on the bag and the freedom that can come with making a decision, however difficult, could carry him through.
How well he plays is up to him. The player might want to blame the caddie for a bad shot, but really, they all know that ultimate responsibility rests with them.
Longer term, the decision about a replacement will loom large. The caddie job is not just about the glory of walking up the 72nd hole watching his player waving to the crowd and accepting plaudits for a victory.
The hours standing by while the player hits practice shots, the time spent travelling, the measuring up the course week after week, and putting up with variable moods of the boss depending on how well he’s playing, can strain a friendship.
Does Diamond want that? Does McIlroy? The next two tournaments will reveal more.
For what it’s worth, the last time McIlroy announced a break up in his personal relationship was in May 2014 in the week of the BMW PGA Championship.
He ended his relationship with fiancée Caroline Wozniacki.By the Sunday, he was the new champion and 2014 was to yield more success in The Open, the Bridgestone Invitational and the US PGA.
McIlroy has gambled and put himself under pressure to perform. Crazy as it seems, it might just work out well.