Belief is a strong and powerful force in a sports team.
It can allow for things to happen which seem unlikely, even impossible.
How can a nation ranked 122nd in the world beat a country ranked tenth which just happens to be playing its biggest games of football in 35 years?
How can New Zealand possibly beat Peru?
The answer is belief.
This New Zealand side actually believes they can defeat Peru.
And they're not just saying it for the cameras and microphones. They firmly and honestly believe it.
When defender Michael Boxall looks you in the eye and says they were gutted not to beat Mexico at June's Confederations Cup, you believe him.
"All the boys have belief in each other and talk to each other. It was a good result," said midfielder Bill Tuiloma after Saturday's first leg 0-0 draw with Peru.
"But that's not enough for us."
And in those six simple words lies the change in the All Whites' mindset in the past few years.
These players are no longer content with just being on the same pitch as the world's best players and teams. Once there, they want to show they belong. They want to win.
Ryan Nelsen instilled belief in the New Zealand team that won qualification and then went unbeaten at the 2010 World Cup. At that time, he was one of the few members of the squad playing at the very top level.
Now, several members of the New Zealand roster are at good clubs in top leagues. There are two English Premier League players in Winston Reid and Chris Wood. Tommy Smith's Ipswich Town are also pushing for promotion. Ryan Thomas starts every week in the Dutch top flight and Marco Rojas is making good progress there, too. Boxall, goalkeeper Stefan Marinovic and others are in the MLS.
These players are paid to do a job each week - win football matches. When they come together as a national team, the same mindset prevails. These guys want to win, regardless of whether they're playing for club or country.
They're quietly pleased with how they went on Saturday, but nowhere near satisfied. That won't come unless they complete the job in Lima.
Practically nobody in the footballing world thinks they will.
But the New Zealand players believe they can.