The challenges of coaching against your countrymen were perfectly encapsulated for Scotland's defensive coach Matt Taylor in last year's dramatic quarter-final loss to the Wallabies.
The Queenslander, who helped guide the Reds to Super Rugby glory in 2011, is adored in Scotland, where his young family is firmly settled, and he's a highly valued member of Vern Cotter's coaching staff.
On Saturday, he'll want nothing more than to see Australia's grand slam bid derailed at the hands of his plucky Bravehearts.
But victory won't come without its share of heartache.
In the dying minutes of the quarter-final in 2015 - and moments before the game-deciding penalty slotted by Australian No.10 Bernard Foley - Taylor was grappling with the mixed emotions of a thrilling finish.
Veteran Wallabies and Reds prop James Slipper had come off the bench and thrown a careless intercept with Australia deep in their own half, which led to a try to Mark Bennett and gave Scotland a shock lead with minutes to go.
As Scotland's defensive coach, Taylor was thrilled - his team, he thought, was through to the semi-finals.
But then he remembered his longstanding friendship with Slipper.
"At the time I was so happy for us as a group because I was thinking, with four minutes to go, that we had a good chance of winning," Taylor said.
"And from a personal level, I probably felt for (Slipper) a little bit because I know him pretty well and to give that pass...
"It's always a funny one against Australia. A lot of my family, who are Scottish, will all be going for Scotland.
"Then there's a number of them at home who are quite proud Australians as well."
Taylor intends to catch up with a selection of his good friends at the Wallabies for dinner on Thursday night before Saturday's showdown at Murrayfield, with Slipper likely to be among the party.
"But there'll be no talking about tactics or giving away too many secrets," Taylor said.
He also indicated he was in no rush to return to Australia, having left after finishing his role as the Reds' defensive coach during their Super Rugby win in 2011.
"I love it here. I've just signed on for another two years with Scotland and I'm hoping if everything goes well that I get through at least to the World Cup," Taylor said.
"My family's very settled here, my kids love it here and I love it here, but I suppose rugby coaching in any regard, you're just on to your next contract, aren't you.
"I feel like I've got a lot to offer Scotland still."