That's how it is at this level - the All Blacks are about continual improvement and don't tend to work with players who carry a whiff of being past their best.
The All Blacks operate without fear or favour; without sympathy or empathy and most certainly not with any sense of nostalgia.
It's a cut-throat business and it moves with frightening speed. Aaron Smith was the little bloke at the Highlanders who occasionally got 10 minutes at the end of games in 2011. Four years on and he is the pre-eminent halfback in world rugby: the catalyst for the speed and width with which the All Blacks play.
Brodie Retallick was a big lug in the age-group game during the last Cup - but barely known outside of it. He comes into this tournament as World Rugby's player of the year.
The list of players not in the All Black frame in 2011 who are now integral and established parts of it goes on and on. This is how it is in New Zealand - the development programmes work. Talented juniors are taken and good players come out the other side and make irresistible claims to be All Blacks.
For those, such as Dagg and Jane, who have had a good run, it's a near impossible business clambering back on board after falling off. Liam Messam is one of the few players who has managed it, but the chances of either Dagg or Jane emulating that are low.
It's an uncomfortable truth, but Dagg has been on the slide for a long time. The way things have turned out, it may actually have been that he sold a vision of himself in 2010 and 2011 that wasn't actually a fair representation of what he was all about.
There was magic in his every move back then, genuine pace and adventure and like many players willing to take risks and back himself, he benefited from a little luck.
That spark has slowly faded since the last tournament, though. It's hard to know why, but perhaps his confidence has been drained by being part of a Crusaders team obsessed with shovelling the ball laterally.
Maybe he could shift Super Rugby allegiance and find that missing spark: get his hands on the ball more and remind himself that he has something special to offer.
But it's not a bet anyone would rush to take. Dagg has looked a long way off being the player he once was. His journey of rediscovery looks like being a long one and in the interim, the likes of Waisake Naholo, Julian Savea, Ben Smith and Nehe Milner-Skudder are offering all sorts of skills, tricks and special features.
Like Dagg, Jane was also in that special player category. Back in 2008, he was the Milner-Skudder of his time - a smaller wing, yet strong, fast and more than capable of imposing himself.
Jane was a revelation, always a joy to watch, but at 32, his time is probably up. Naholo, Smith, Milner-Skudder and Savea are not only the present, they are the future.
Dagg seemed to agree as much when he Tweeted: "Gutted to not be in the RWC2015 team but congrats and all the best @AllBlacks men. it's been a hell of a journey cheers."
Cory Jane
Age: 32
Debut: v Australia, Hong Kong, 2008
Most recent test: v USA, Chicago, 2014
Tests: 53 (45 starts)
Tries: 18
Israel Dagg
Age: 27
Debut: v Ireland, New Plymouth, 2010
Most recent test: v South Africa, Johannesburg, July
Tests: 49 (46 starts)
Tries: 14
