Eales and co showed the kind of character that had seen them become global greats in 1999 and would secure Tri Nations glory shortly after the Lions left for home and the former star second row reckons more of the same will be required this time around.
"It's a physical challenge, but it's also very much a mental challenge. And they have to win both," Eales told Rugby Gold.
"One of the things is that - and they got a bit of a taste of this against the Welsh last year - when you play against the same team three weeks in a row, that's a totally different challenge from playing against a side three times over a two-month period.
"The challenge of being able to step up to the mark and really judge each week where you have to improve, what have the opposition have been doing and then anticipate that and knock them off, it's a big challenge.
"This is a once-in-a-career opportunity. They don't come back."
Those sentiments were echoed by another Lions heartbreaker from the first tour of the 21st century, Rod Macqueen.
Macqueen was coach of that Wallaby side in '01 and he is urging current boss Robbie Deans to remind the new breed that what lies around the corner has no parallels or pre-cursors.
"They have to realise that this is going to be different to any other game they play - totally different," said Macqueen.
"It's totally different to most Test matches and a World Cup. It's totally different altogether."