They began their careers together in Wellington as rivals - Smith the new kid from Taranaki and Nonu the age group player who quickly made an impact for the Hurricanes and All Blacks - but ended up as long-term midfield partners and mates. They have played a world record 58 tests together, a mark brought up against Argentina at Wembley, but Nonu's shoulder injury prevented them from extending it this morning.
Asked if he had to work harder than other players to get to where is now, Smith, a qualified lawyer, said: "I think I had to work harder for less reward. I never made an age group side and people say to me now 'you're not the one often getting awards' and things like that.
"And that's fine, I've learned to live with that, probably because that's what happened when I was young. That's never bothered me. I find my motivation through the team and people I play with. That's far more important to me than personal ego.
"Even now, walking away from it, it's going to be tough. There are things you're going to miss and some you won't, but just being involved in teams and playing the game you love with a bunch of lads that are your best mates - it's a pretty cool life. I'm like most Kiwis, I grew up dreaming of playing for the All Blacks so to live that dream - you realise how much hard work it is when you get there - but it's still a dream to pull on that jersey. You have a country behind you and not many people can say they have that, not even other professional sportsmen. The team they play for isn't as unique as the All Blacks are.
"Walking away, I know it's going to be the right thing, but it doesn't mean it's going to be easy."
Smith, 33, is one of seven All Blacks leaving after the World Cup. Nonu is another, as is Dan Carter, Richie McCaw, Tony Woodcock, Keven Mealamu and Colin Slade.
Slade is a relative newcomer but Smith has played with the other six since making his debut against Italy in 2004.
"The good thing about a World Cup is that it's such a massive challenge in itself so I haven't really thought about it [leaving]. Maybe if this was an end-of-year tour then maybe there would have been a lot of that. Speaking for the other guys, there hasn't been a lot of talk about the fact this is the end. We're aware of it and I'm sure the rest of the team are, but for now the challenge is bigger than any individual.
"When you look at the five or six of us moving on, when I started we were all together so that's pretty special when you have a group who have played 12 or 13 years together."
If Smith is the glue which binds his team together, Nonu is the wrecking ball which takes apart the opposition. In other words, they are perfect partners.
"We started as rivals and now, with the record number of test matches together, it's cool to think where it's come from and finished. It's a special journey and he's a pretty close mate now. I know it will be awesome when he does get that 100 and hopefully I'm there to enjoy it with him."