Paul McCartney has been thinking over what Malcolm Gladwell said about him in Outliers, a non-fiction book that tries to define the ingredients of success.

"It's funny — I was talking to someone about that, because I've read the book. I think there is a lot of truth in it," McCartney said in an interview with CBC's Q cultural affairs show that aired Friday, ahead of his appearances in Canada next week.

Gladwell cited the Beatles as proof of his 10,000-hours rule — that one of the predictors of success in any field is practising the task for 10,000 hours, just as the Beatles did in the 1,200 gigs they played in Hamburg from 1960 to 1962.

"I think in our case, we always said 'Man, we had so much practice that by the time we got famous, we really knew what we were doing, and we were a good cohesive unit as a band,'" McCartney says.

He admits he's "not a great one for theories."

'I'm in a very interesting stage. I'm loving singing. I can't believe that I'm doing nearly three hours without taking a [breather] or anything.'—Paul McCartney

" I mean there are a lot of bands that were out in Hamburg who put in 10,000 hours and didn't make it, so it's not a cast-iron theory," he says. "I think, however, when you look at a group who has been successful … you always will find that amount of work in the background. But I don't think it's a rule that if you do that amount of work, you're going to be as successful as the Beatles."

Canadian wordsmith Gladwell finds no hard and fast logic behind success — there are too many random variables, like personality and when and where an individual is born and just plain opportunity.

For opportunity, there have been few careers like McCartney's — the man called by the Guinness World Records the "most successful musician and composer in popular music history." He's still singing 40 years after the breakup of the Beatles, putting in three-hour shows without obvious effort at age 68 and still enjoying it, he says.

McCartney, left, relaxes backstage with his band. (MPL Communications)"I'm in a very interesting stage. I'm loving singing. I can't believe that I'm doing nearly three hours without taking a [breather] or anything. You assume that you'd be feeling it now and that maybe you'd get fed up with it, but it's just the opposite," he says.

He's well past his 10,000 hours — so far over that he admits he doesn't analyze what stage of his career he's in or even think very far ahead when he takes a booking. Yet he packed 500,000 people into an outdoor show in Kiev, Ukraine, in 2008 and popped into the East Room of the White House for an intimate concert for Barack Obama and a few others in June.

Birthday surprise

He even managed to surprise his old bandmate Ringo Starr at a Radio City Music Hall concert in New York that fell on Ringo's 70th birthday on July 7. For Starr, it was a regular performance of his All-Starr band, which in its current incarnation draws on the talents of Edgar Winter, Rick Derringer of The McCoys, Wally Palmar of The Romantics, Richard Page and Gary Wright.

Ringo's brother-in-law, the American musician Joe Walsh, wanted to make McCartney's appearance a surprise, suggesting he hide out in the back stalls of the theatre and sneak on at the end.

"I've never actually seen his All-Starr show," McCartney says of that night in July. "I was enjoying the show along with the audience, but when it got to A Little Help from My Friends, the people in the row in front of me were looking at me like 'What's happened? Shouldn't you be up there as one of his friends?' I'm going 'Shh!'"

McCartney and Ringo Starr are shown together in June 2009. McCartney surprised his old friend on Starr's 70th birthday. (Kevork Djansezian/Getty Images) Ringo thought the show was over after his grandkids had come on with a birthday cake. McCartney says Starr's wife, Barbara Bach, had to hold him back while Walsh struck up Birthday and McCartney came forward.

"Ringo did not know. I swear he was just so gobsmacked," McCartney says.

"[Ringo] said 'I'm going to the dressing room.' She said 'Hang on just a minute.' And then we started up Birthday with Joe Walsh and the band, and then he finally realized what was going on. He came leaping back on stage and said 'I wasn't going to sit that one out.'"

Valuable friendships

McCartney said he appreciates his friendship with Starr more as he gets older.

"We went through a kind of sticky patch when the Beatles were breaking up, and there was a lot of talk, and people were setting us against each other. Outside of that patch, we've always had a really good relationship," he says. "I think as you get older, you just realize how valuable your friends are."

McCartney's touring is taking on a different shape these days because of his commitment as a parent to six-year-old Beatrice, his daughter with ex-wife Heather Mills. He spoke to CBC from near Hastings in southern England, as he drove to pick up Beatrice from a playdate — yes, the phone was hands-free.

"Because of my personal circumstances, I spend a lot of time looking after my six-year-old girl, and for that, I'm a pretty hands-on dad. So I said to my promoter, … 'These are the weeks I can work, and these are the weeks I can't work, because I'll be getting up in the morning seeing my little one off to school and stuff,'" McCartney says.

The promoter wasn't all that keen on the arrangement, but McCartney knows he's at the stage where he can pick and choose, and he chooses life without tours lasting three to six months.

Still sound fresh

" It actually works great really, because … we do less work and … we're doing exciting events, so we're much hungrier to play," he says.

McCartney and his current band play a set that mixes hits from his time with Wings, his long solo career and new material with the old favourites like Long and Winding Road and Yesterday. Yet McCartney says even now the Beatles songs sound fresh to him.

"I think one of the tricks is that I don't do them that much. So I find myself, when I do sing them, actually looking at them," he says.

"You have to take a moment and go, 'Oh, this is how this one goes.' … I'm looking at the writing from my perspective now, because … I'm looking at a 24, 20-something young man writing these things and I'm thinking, 'That was pretty mature or that was a good little line.'"

McCartney played a concert on the Plains of Abraham in 2008 for the 400th birthday of Quebec and then was in Halifax last year. He also has clocked some historic firsts in recent years, such as his 2005 concert in Moscow's Red Square and playing to the International Space Station in 2006. It's not that he seeks out new frontiers for live performance — it's just a question of opportunity, as Gladwell would say.

"It's a not a kind of conscious decision, but what happens is, if somebody makes an offer to play … the Quebec gig to so many people for a sort of a special occasion, then it's very interesting. I'm very lucky, I get these offers," McCartney says.

"Somebody says, you know, 'Would you like to play for the Space Station.' I say 'Are you kidding?' So we do it. As I say, I feel very lucky to have the opportunity."

Concerts and studio albums are what McCartney calls his "day job," but he is indulging some of his many long-time interests and has some new projects on the go, among them writing music for a ballet. He has not yet revealed which ballet company approached him.

"One thing that's coming up next year I'm working on now that I haven't done before is I'm very interested in photography, and I've got a project at the moment that might end up as a photo exhibition," he adds.

McCartney plays the Air Canada Centre in Toronto on Aug. 8 and 9 and the Bell Centre in Montreal on Aug. 12.