To rack up more than 400 first class games in both rugby league and rugby union it is pretty clear - there must be a love of the game.
Brad Thorn has that. That fire of passion has been flaming ever since he was a youngster and even now at 38 it still burns intensely.
For Thorn, competition, and the desire to put maximum effort into everything, is what drives him.
''I just love footy. It is passion. Often with guys they will get injured and stuff and they will have to call it a day. For me I haven't. What it comes down to is I have a love of competing,'' he said.
''Do I still want to put the hard work in? Do I still want to try and achieve certain things? The answer to that is still yes. I love training my butt off and competing.
''How do I do it? I just get on and do it. I have been very lucky with injury; luck is a big part of that.
''For me it is a way of life because I have been doing it for so long. I have almost been institutionalised. It is what I have always done and I love doing it. The body is saying to me it still feels pretty good, there is still a demand for me to play at this level.''
Thorn made his first class debut in league for the Brisbane Broncos in 1994, when his present team-mate, Jason Emery, had yet to have his first birthday.
Thorn has played 450 games at the top level, and won nearly everything in the game.
He has been called the ultimate professional and says that his long career can be put down to a combination of things.
''I could break it down. A couple of years ago [All Black doctor] Deb Robinson wanted to check my shoulder. She saw on the scan. 'You have dislocated your shoulder, when did you do that?'
''I said, 'I don't know what you are talking about.'
"She said, 'No, you have done your shoulder.' I said,'I have never done that.'
"She said, 'When it comes out it smashes against the bone and there is a little divot there that is created when it comes back in.'
"I said, 'I'm telling you I have never done my shoulder.'
"She said, `You must have dislocated it and it has gone straight back in. Because you have so much muscle around there it has just locked it back in.'
''I had never known.
''So she said, 'Sit down and think about it.' And sure I had a few big hits in that area over the years ... Maybe someone else who was not strong in that area it would pop out all the time and, who knows, they would have to get a reconstruction.
''But, genetically, from Mum and Dad, I am lucky. I am a decent sized guy, I do not seem to get injured much. So you have that part, maybe 33%.
''Then the next 33% is I work hard on weights. I strap my ankles, even though I have never had an injury with my ankles, so I am giving myself every chance. It is not just about lifting weights so I can palm guys off. It is armour. That is a big part of it. I stretch a lot, even though I am grand daddy, my muscles are supple. So that is 66%.
''And the last 33% is probably luck ... I am right in the thick of it. There are so many different positions you can get hit. So that is luck. Something could happen. Everything I can do within my power I am doing and the luck side of things helps. And I have been lucky.
''I have over 20 years of training ... I started young and my body got used to it. I was always conscious of that sort of stuff, ice bathing, stretching and that sort of thing.
''Even before I became a pro footballer. I was 17 at the time - it is funny to talk about - there was a footpath and grass next to it and I always walked on the grass. It was all about my knees and my ankles, keeping them healthy.
''That is a young kid who had his mind on wanting to achieve something. It probably did nothing for me, but I am just saying that was my mindset. This is what I wanted to do. These things are important and I want to give it my best.
''It was probably nothing, but the knees have gone OK.''
Even now, Thorn said, after he puts his four children to bed, he will drive to Moana Pool, get under the waterfalls in the leisure pool and let the water pour over his body to soothe the muscles.
''My motto that my Dad gave me when I was young was reward for effort. The greater the effort the greater the reward ... that is how I sort of roll.
''You've got to be smart with it too. If you just go out and flog yourself ... sometimes you need to be smart how you put that effort in. As I have got older you can't just flog yourself or you will get burnt out.''
The big lock played his first Super rugby game in 2001, when the Crusaders were thumped by 50 points by the Brumbies in Canberra.
He was green back then but nine rugby seasons later he is a seasoned rugby player.
But when will it end?Thorn admits it is time for a break after the Highlanders season ends.
''The last two years I have not had a break at all. Two thousand and eleven - it was tough. It was massive. I am still riding on that in a way. There was no real break after that. The All Blacks had three months off after the World Cup. Remember I was on my knees in tears after that World Cup.
''One week later I'm in Japan in a one room apartment waiting to play in front of 3000 people in a 50,000 seater stadium with guys I don't know and I don't know the language.
''I have decided at the end of this competition [Super 15] I am going to have some form of break. Two to three months to rest my body. I guess the way the season has gone so far is probably not how I had planned for it to go. There is still a want for me here. To come back and rectify it a bit.''
Thorn still wants to play and coming back to the Highlanders next year is still an option, especially as his family really enjoy Dunedin.
''Coming back here meant a lot to me. I wanted to contribute on and off the field to this team. I feel I have done that, both on and off the field. The results have been disappointing, obviously, so it would be nice to be part of some improvement on that. But it is something I want to think about.''
The Highlanders are winless after eight games and Thorn says it is not foreign territory for him.
''In 1999, with the Broncos, we lost something like nine out of the first 10 and that was with a dream team - Alfie Langer, Darren Lockyer, Gorden Tallis, Steve Renouf. We were fighting hard but not just quite getting there.
''But often that is when you learn a lot. You ask hard questions of yourself and you come back stronger at some stage. Whether it be some time later that season or the next season, or whatever.
''That next year with the Broncos we lost four games all season and won the grand final.''
Iron men
Players with long careers (first-class games)
Sir Stanley Matthews (football) 795
Ryan Giggs (football) 725
Steve Menzies (league) 511
Darren Lockyer (league) 458
Brad Thorn (union/league) 450
Sir Colin Meads (union) 361
Brett Favre (American football) 321
Brad Thorn career games
Brisbane Broncos 214
Crusaders 92
All Blacks 60
Canterbury 30
Fukuoka Sanix Blues 16
Queensland 14
Australia 8
Leinster 8
Highlanders 7
Tasman 1