But the three-time major champion told an Irish newspaper he is stunned at the recent disclosures about Woods' personal life and like others is trying to come to grips with how the indiscretions occurred with few of his peers knowing.
"I'm amazed by the fact I am out on tour and I knew nothing. I'm wondering, 'I must have my head in a hole or something', but seemingly nobody knew anything," Harrington told the Irish Times in an interview at his Dublin home.
"That's what amazes me, I thought the guy was, and I'm particularly loath to use the word, but let's say had a quiet life, went back to his hotel room every night ... [to] sit in your room for six hours is not a pleasant experience, he couldn't go out. "I felt sorry for him in that sense, [because] I could go out [for dinner] every night. I assumed life on tour was real tough [for him]. You knew when he was off tour he enjoyed his boat and going fishing and that was the only freedom he ever got.
"I'm amazed by both sides, that if somebody goes down that road you usually can tell, there's a bravado in it and all that sort of stuff ... the odd time he'd be in a hotel and you'd see him going getting his ice to have an ice bath for his knee and things like that, you'd see him in the gym, always just incredibly diligent.
"You'd kind of often think [of asking], 'do you want to go out for dinner?', and not [ask], think he is trying to do his own thing and trying to be special in that sense. I felt for the fact he was absolutely in a fishbowl, life was tough in that sense.
"The only thing I can give on the whole story is wow, I was out there on tour with him for 10 years and often Tiger himself has said I'd be [considered] a friend, and I had no idea this was going on in his life ... a triple life: golf, home and when he was away."
Harrington struggled for most of 2009 until contending often toward the end of the year, including a memorable duel with Woods at the WGC-Bridgestone Invitational. Harrington led with three holes to play, only to hit his third shot into the water after a controversial slow-playing warning.
Woods went on to win the tournament, then took the unusual step of calling out the referee for causing Harrington to rush and make the mistake that led to a triple-bogey 8.
They were also in contention the following week at the PGA Championship, where Harrington failed to defend his title and Woods, despte a third-round lead, failed to win his 15th major championship.
"I expect him to win 19, I don't think this changes him as a competitor," Harrington said. "It might make it tough for him to play regular events when he comes back, but the majors have always been different ... I don't see this making any difference going forward in the majors and maybe it might clear up one or two things that could have been emotionally affecting his game in the past ... from a purely selfish point of view, his life needs more clarity, emotional stability and balance if he wants to bring it to the golf course, maybe that's the reason -- I didn't see it myself -- why [people say] he was angry on the golf course for the past six months."
Bob Harig is the golf writer for ESPN.com.