Foster said it was simple: "If you are not at your best, you lose."
"It sets things very simple and clear in your mind at the start, but to have two [Tests] in a row here is something special for this team.
"We're determined to prove this team's got the character to grow from our last series and the frustrations from that."
After the July series, all the southern hemisphere sides had something to prove in the Championship.
"We can't wait and there's no better place to start it than over here," he said.
"We're focused and determined to improve our game and put a performance on that we're proud of. But it gives you great clarity when you come over here because you know the size of the challenge is going to be massive, and you've got to give everything.
"We're a team that's growing its game. I think we're still developing. We've got some good insight into what we want to do, but we've got to get better at executing it. The focus of the boys has been on that space."
Foster said it was wrong to pigeonhole the Springboks' game plan as limited to beating teams up then kicking the ball and chasing.
"They are very good at that, but they are also very good at moving the ball around.
"They've caused us issues in the past with some of the width play they do. And some of their round-the-corner plays. They're not world champions just because they're good at one thing – they do a lot of things really, really well.
"Under pressure there's some go-tos that they fall back on and they try to be clinical in that way."
Foster said South Africa would try to move New Zealand around to attempt to bring the altitude factor into play, especially in the first quarter.
"We've got to be up for the variation that's coming."
Wing Caleb Clarke returns to the starting side after being frustrated by a hamstring injury that kept him out of the Ireland series.
"It has always been our plan to get him back on the park as soon as we can. He hasn't played rugby for us for a long time with the break he had last year with Sevens.
"We just want to get the ball in his hands. He's still learning at this level. I'm sure there'll be a mistake or two but reality is that he's an exciting player for us."
Samisoni Taukei'aho at hooker was a player who was progressing well. He had good role clarity and a clear mindset and loved the challenge.
"Going into a big game like this he's got a clear head. I back him, he's shown off the bench he can make a big impact, and it's a great chance for him," he said.
Injuries to Ofa Tuungafasi, Nepo Laulala and Brodie Retallick had forced changes with Angus Ta'avao starting on the tighthead and Scott Barrett partnering Sam Whitelock in the locks while Ethan de Groot and Tyrel Lomax will be on the bench.
De Groot got his chance with Aiden Ross suffering a calf strain. He had trained hard over the last six weeks to achieve the goals the selectors wanted from him, and he was in a good space.
Blindside flanker Shannon Frizell is also on the bench. Foster said he had been the form player in the position in Super Rugby until his injury. They needed size and set-piece options in the 23.
They were working with new forwards coach Jason Ryan who had done well since joining the side.
But Foster warned Ryan didn't have a magic formula, it was a process.
"He's made an impact in a couple of areas we know he's good at, and he's already got a bit of movement with our players."
However, he had kept his mandate focus narrow to start with, but it wasn't just about the forwards - it was the team overall.
"You have to play physically against the Boks, but you also can't get fixated on that."
The All Blacks need to be smart in looking for opportunities.
"We're making sure we look at the game holistically rather than focusing on just one area."