[engnr567]

One key thing about the result is that it doesn't mean that the probability of survival is 30%. The prison director can choose an arrangement such that the strategy is guaranteed to fail. If the prison director is intelligent and after your life, you are infinitely more likely to survive by opening boxes randomly.

[zwkrt]

The prisoners in the game can collude before the game begins, so they can create their own ordering on the fly. This cannot be overcome by the warden.