"We must all hang together or we will all hang separately."- Benjamin Franklin
It's about team work and selfishness. Everyone wanted to box, so they all fought each other to have possession of it. One person finally realized that he could just kill everyone else and have the box all to himself, however upon killing the other people there was not enough weight to move the box. It ended up on the other side of the platform than him and to move towards it would tilt the platform and cause the box to fall off. In trying to get the box all for himself he killed everyone else and assured that no one would ever have the box, including him.