Esterhuizen promises no let-up from Springboks
The Springboks have won the last two World Cups and backed up their 2023 triumph with five wins out of six against New Zealand, Australia and Argentina in this year's southern hemisphere Rugby Championship.
Rassie Erasmus's imposing team will be firm favourites to defeat Scotland, England and Wales over the next three weekends, with the Springboks opening their November campaign at Murrayfield on Sunday.
But Sharks centre Esterhuizen, speaking at the squad's Edinburgh hotel on Wednesday, said: "For rugby players, it's one day you can be at the top of the world, the next day you can lose to anyone.
"So, yes, it's good to have confidence and a bit of an aura, but also you know that any team in the top 10 could probably beat you on any given day.
"And that's rugby. We just focus every week on being the best we can that week and obviously, strive to be better. You can't always be at the top and think you can't get better."
South Africa won last year's World Cup -- a record fourth global crown -- following a remarkable trio of three straight one-point wins in their quarter-final, semi-final and the final itself.
"A lot of people say, 'it's lucky, it's this, it's that', but I know obviously South African players' mindset is, even if we're down and out, we're going to keep on fighting until the end," said Esterhuizen.
"We always have that mindset to fight through every battle, through every game. It doesn't matter how close the margin or if you're behind or in front, you keep on fighting, you don't rest."
South Africa began their 2023 World Cup with an 18-3 win over Scotland in Marseille -- a result Esterhuizen insisted was closer than suggested by the scoreline.
"The game at the World Cup wasn't a walk in a park," said the 30-year-old.
"It was still quite a tough battle. Half-time we came in, it was 6-3, it was very close. You can always expect a tough battle against Scotland."