The world number one spoke to media in his first major press conference since storming off the green in Florida.
The 23-year-old played the opening eight holes of his round in seven over par, before finding a water hazard on the 18th and immediately quitting the tournament.
At the time McIlroy said he was "in a bad place mentally" but later released a statement which said he could not play on because of wisdom tooth pain.
I was all over the place and I saw red and it was a mistake. Everyone makes mistakes and I'm learning from them.
When asked which of his excuses was the truth McIlroy said on Wednesday: "It was a build-up of everything.
"Mentally my head was all over the place but at the same time I've been struggling with my wisdom tooth for over a year.
"My tooth was bothering me, but it was not bothering me enough to probably quit, but that's just the way," he added.
The Co Down man told journalists walking off was a mistake but the nature of his job means he makes most of his slip-ups in the public eye.
"I regret what I did, it won't happen again," he explained.
"There's no excuse for quitting and it does not set a good example for the kids watching me."
After a year of record-breaking victories and playing as part of a winning Ryder Cup team, McIlroy admitted to feeling the pressure to continue his impressive form.
"It was a build-up of high expectations from myself, coming off the back of such a great year last year and wanting to continue that form into this year and not being able to do it. It all got too much," he said.
No matter how bad I was playing I should've stayed out there. I should've tried to shoot the best score possible even though it probably wasn't going to good enough to make the cut.
Looking back over his career, McIlroy said it "probably" was not the first time he had stormed off mid-game, adding that as a teen he had contemplated quitting golf altogether.
"I was working so hard and not really getting much out of it," he said.
"When you start to enjoy your golf you play better and I have not been enjoying it because I was putting so much pressure on myself.
"I learned that when the going gets tough, I've got to stick in there a bit more and I've got to grind it out."
The young player, who is preparing for the golf's first major of the year - the Masters, denied his new equipment was behind his drop in performance
McIlroy's sponsorship with Nike began in January and it has been rumoured that the change in club and balls had a detrimental effect on his game.
But knowing a poor workman blames his tools, McIlroy revealed he is happy with the equipment.
"If you strike any golf ball in the world correctly, it's going to go where you want it to.
"When I hit a good shot I know it's all me, nothing to do with the equipment, nothing to do with the ball."
I feel like I let a lot of people down with what I did last week and for that I'm very sorry.
He added he was working on a swing change to correct his play, commenting that there are "no quick fixes" in golf.
The golfer's love life has long been tabloid fodder, and his relationship with tennis champ Caroline Wozniacki has been played out in public. As his performance nosedived, some speculated his relationship had also taken a downturn.
However, McIlroy denied events off the green had affected his play.
"Just because I have a bad day on the golf course and Caroline has a match in Malaysia doesn't mean we're breaking up."
"Everything on that front is great," he added.