I will try to explain from perhaps a different perspective: in a attack one player has the ball and fourteen have not. This may sounds obvious but how many players can the ball carrier actually pass to? One? Two? How predictable is your play? Can your opponents defensive be ready?".
Australians started with two things: playing very close to the tackle line (putting themselves under pressure!) and giving the defense backline something to think about: decoy runners.
This means a lot for us coaches:

explain the tackle line / gain line principles to your backs

show how technique helps bringing the tackle line closer to the gainline

alignment of all the backs should be such that the ball carrier has at least two players on his outside to pass to

support runner should stay on the inside (ask your players: where do they come from?)
Within the Adaptive Game plan we learn players to adapt attack to defense, this is an important part of that: not simply execute a set move but present the defense with options, they will always make the wrong defensive decisions!
Exciting stuff, one of the reasons I like coaching the youngsters. Hope this helps, be careful just copying the brumbies...".