Only thing is, Wax is above them at the time, so his weight is going to be applied downwards, if you're holding something above your head and it tripples in weight then you probably have to put it down, or drop it all together, it wasn't that the force you were exerting to hold it up got weaker, it was that the force needed to hold it up became greater.
In other words, the force of the push didn't have to change, he was simply harder to move than the nails.