World number one Scheffler became a father for the first time last week when his wife Meredith gave birth to a baby boy.
But with McIlroy filing for divorce from his wife Erica in Florida on Monday, Harrington is not convinced anyone can make a prediction about how the world number two might react as he bids to win his fifth major after a near 10-year drought.
“There was a guy who wrote the gambling book once and he said if the first hild is a boy, you’re going to have a winning year,” Harrington said of Scheffler. “So yeah, there could be a big euphoria from having a new baby boy.
“It’s not like he wasn’t in a great place before that. But you could be in a phenomenal place because that could really work in your favour.
“Obviously, with Rory, you know, there could be clarity there for him. But he’s won the last two weeks so I don’t know. I have no idea.
“You know, it’s all very personal. I’ve seen people who’ve had stuff going on off the golf course and the golf course becomes a haven. Nobody can ask them the question out there. They are back at business as usual.
“But then I’ve seen others where, you know, just being out there, they weren’t comfortable. So I just don’t know where it’s going to sit. And it’s impossible to tell.
“There’s no way anybody can tell me that there’s a guaranteed, set cause and effect. There never is in golf.”
Rory McIlroy has filed for divorce from his wife Erica Stoll
Harrington dealt with a huge distraction in the build-up to a major himself, famously overcoming a serious wrist injury to win back-to-back Open Championships at Royal Birkdale in 2008.
He’s now 52 and while he knows that winning a fourth major is a long shot in the eyes of many, he’s not in Valhalla to make up the numbers.
“I was thinking about it the other day,” the Dubliner sad after a practice round with Tommy Fleetwood, Shane Lowry and Jon Rahm. “Somebody said I had 40 second places in my career and I was saying, would I like another second place.
“Sometimes a second place might not be so bad. But I know if I finish second, I’ll hate it. So I am trying to be resigned to just doing my stuff and doing it right.
“I haven’t got many years left of being able to be competitive. So I’m just trying to do my stuff right and see where that goes rather than put a result on it.
“I know I played three majors last year, made three cuts, and people said well done to me, and that was frustrating.
“So yeah, winning is what it’s all about; being in the hunt, being under pressure. If I didn’t think I could win, I would probably come anyway.
“But I certainly don’t feel like I’m there yet. I’m being nice to myself by saying that I’m trying to catch lightning in a bottle. But I don’t believe that.”