That's the verdict from English performance coach Paul Boross - "the pitch doctor" - who says the bonding element of the haka gives the All Blacks a significant edge.
He told The Guardian's Robert Kitson that "what happens immediately before a game - during the anthems, in the final moments before kick-off - can make an enormous difference in a way few people understand."
Boross said: "Everyone talks about the haka being a war chant and being there to frighten the opposition. Actually what it's doing is bonding them psychologically and physically into a tight unit. I've had whole sports teams, before they go out, just breathing at the same rate. It makes them feel connected and builds rapport."
On the subject of unfair advantage, Boross said other teams should find ways of emulating the All Blacks' pre-match ritual, and had specific advice for Wales.
"I don't think working yourself up into a good state is any kind of unfair advantage. More fool everyone else for not doing something similar. You don't have to do a haka but you can do something that creates the same feeling."
Kitson quoted another motivational expert, former English cricketer Jeremy Snape, as saying opponents needed "to see it as a ceremonial show rather than a psychological advantage", presumably to counteract its effect.
Boross advised Welsh coach Warren Gatland to get former forward Scott Quinnell to deliver a pre-match speech.
"If you've been in the room during one of his team-talks it's extraordinarily moving. ..why wouldn't you use somebody with that passion to wind them up?"
