If you want to give multiple people access to unlock the chain without giving them all the same code, you can chain combo locks together. Everyone knows one of the combos and can unlock the chain at their point. He’s saying eventually someone screws up or betrays the system by re-locking both ends of the chain itself, which locks out the other participants.

I don’t understand how the contraption in the picture works, but apparently it solves for this issue

And then he calls out the model of lock as easy to pick