On Wednesday, Rory McIlroy said, "Golf is a very fickle game and it can humble you quite quickly."
By Friday at the BMW PGA Championship in England, McIlroy had proven his words true.
After an opening 71 at Wentworth Club, McIlroy exploded to 6-over 78 on Friday to miss the cut in his title defense, just five days after winning the PGA Tour's Wells Fargo Championship by seven shots and setting a new tournament scoring record by five.
McIlroy had little to say to reporters after the round, which left the world No. 1 on the wrong side of the cut line for just the third time in his last 45 worldwide events.
The 78 is McIlroy's worst European Tour score since a first-round 79 in the 2013 Open Championship, and worst worldwide since the same tally in the second round of last year’s Memorial.
It seemed clear fatigue had set in for McIlroy, was playing for the fourth consecutive week, including two wins at Quail Hollow and the WGC-Cadillac Match Play. He also finished T-6 at The Players.
The most outwardly emblematic sign of McIlroy's fatigue and resulting frustration came on Thursday when, after a poor second shot in the par-5 17th at Wentworth, he chucked his 3-wood down the fairway. It'll likely result in a fine from the European Tour, and it's a bad look for the Ulsterman, who threw a 3-iron even further and into a water hazard at Doral in March.
Still, McIlroy tried to remain calm about a clearly disappointing outcome.
"I'm not going to read too much into it," McIlroy said. "It was inevitable at some point that the run was going to come to a bit of an end.
“If anything good comes out of this, it's just that I get a little bit of a rest over the next couple of days, and feel a bit fresher for what's going to be a really big week for me next week.”
McIlroy is headed to his home country, Northern Ireland, to prepare for the Irish Open, where he is host at Royal County Down.
Ryan Ballengee is a Yahoo Sports contributor. Find him on Facebook and Twitter.