The All Blacks are so often governed by the most basic laws of physics. None more prevalent than there being an opposite and equal reaction to every action.
It's often sold differently - that one man's misfortune is another's opportunity.
Aaron Cruden may not particularly care for how it's packaged. All he knows is that he started the June series with a No 10 on his back, damaged his neck in the following game and in his absence Beauden Barrett became an international superstar.
It's a reminder that rugby at the highest level is a cruel business. Cruden, having waited patiently behind Daniel Carter for five years, earned that start in game one against Wales. He had plenty of runs on the board scored through the period 2010-14 and he was, certainly at that stage of the season, the form first-five in Super Rugby.
One injury changed it all and Cruden now finds himself in the place where many before him have been - waiting for the wheel of fortune to spin back his way.
He didn't suffer a prolonged collapse of form or loss of confidence. He didn't lose his way or tie himself in knots trying to nail his big chance. He actually played quite well in that opening game and then fate struck in the next one and Barrett pounced.
Cruden isn't suddenly out of favour because the coaches have lost faith. He's not yesterday's man although he may feel a little like the forgotten man while Barrett so rightly fields the accolades and wins the admiration of the rugby public.
It's a hard place for Cruden to be - waiting, hoping that his chance will come to remind the coaches why they had him as their number one only a few months ago.
He has been afforded 55 minutes of Rugby Championship action - which isn't bad for someone who started both tests on the bench, but that isn't really the path he had in mind back in June.
His patience is going to be tested. Right now, it feels like Barrett may never have a bad game: that he's going to ride the wave of form he's in for the rest of his career.
Cruden doesn't come with the same versatility as Barrett but the All Blacks are still, always, going to need genuine first-five cover in their 23. As Lima Sopoaga, the other No10 in the squad, doesn't play any other positions either, Cruden can feel some confidence for now, that he will at least be involved. He will just have to deliver what he can in training. He'll have to work as hard as he always does and when he gets time on the field, even if it's only 10 minutes, he has to do all the things the coaches ask him to do.
That's his only way back in at the moment: accepting that he and not Barrett is now the man who will start tests on the bench and be thrown in at whatever point to lift the tempo and intensity. If he can do that, make the same sort of impact that Barrett used to regularly make coming on later in the game, then he'll at least be giving himself a chance to change his future.The All Blacks are so often governed by the most basic laws of physics. None more prevalent than there being an opposite and equal reaction to every action.