Speaking with reporters in Doral, Fla., where he is entered in this week's WGC-Cadillac Championship, McIlroy offered no excuse for quitting Friday after eight holes of the second round at the Honda Classic Friday, where he had been defending his 2012 title.
McIlroy, ranked No. 1 in the world, shot even par 70 in the first round but carded a triple bogey, a double bogey and two bogeys before leaving the course at 8-over par for the round and the tournament.
He said in a statement at the time he regretted the decision but it was "one I had to make" due to a sore wisdom tooth that made it impossible to concentrate.
He told reporters in Doral Wednesday had given himself "a red card" -- signifying a player's ejection from a game, Golf Digest reported.
"No matter how bad I was playing," he said. "I should have stayed out there. I should have tried to shoot the best score possible even though it probably wasn't going to be good enough to make the cut.
"It was a mistake and everyone makes mistakes, and I'm learning from them," McIlroy said.
He said Wednesday his decision to withdraw Friday "will be a blessing in disguise."
"It was like it just sort of released a valve and all that sort of pressure that I've been putting on myself just went away," he said. "And I was like, [let's] just go out and have fun. It's not life or death out there. It's only a game. I had sort of forgotten that this year."