Exactly. While a PLB will help to get you rescued, it doesn't work instantly, nor can one expect it to be 100% dependable (remember, stuff breaks).

Therefore, it's still necessary to have, at the very least, some knowledge of survival techniques for the environment in which you are traveling.

Along the same lines, it's necessary to have at least a basic knowledge of First Aid techniques to keep either yourself or someone else stable enough that they can be rescued.

Sometimes gear fails, at which point you either have to replace it or adapt as best you can.