The mind games went all wrong for the triple major champion in The Open third round on Saturday and he was less than pleased after a level-par 70 left him down the field on 212, two over par.
"For me, today, 70 was a steal and 69 would have been a miracle," Harrington said on a sun-kissed day at Royal Lytham & St Annes. "I was really at sixes and sevens with my game.
"I got on the practice range yesterday and got something in my head and just really struggled with it today. I didn't show much trust, faith or confidence in anything out there."
Harrington was playing alongside Rory McIlroy and while the world number two was suffering a crisis in confidence, carding a 73 for 215, the 2007 and 2008 British Open champion was saddled with a scrambled brain.
"The first two rounds I thought I played well enough tee to green, I just didn't hit my wedges very well," he said. "I was sorting that problem out yesterday on the range and it certainly got in my head.
"I wasn't settling on any good thoughts at all. I kind of messed with my head a bit," added Harrington.
"My head, my mind was far too active today. I was thinking too much. I didn't know what I was thinking at times out there and that's a position you don't want to be in."
Harrington is now desperate to clear his head in time for the final major of the year, the U.S. PGA Championship at Kiawah Island in three weeks' time.
"That's completely on my mind now," said the 40-year-old who won the PGA in 2008. "My mind is very much focused on getting my game in good shape for Kiawah Island."