The Method
Failure
Push the right muscle to its edge.
Failure means taking the target muscle to its limit: the set ends when that muscle cannot finish one more clean rep. It only counts when the correct muscle is the one failing, not when you are just generally tired, and it never means grinding out ugly reps or getting help to finish them.
That is why Failure comes after Form. You earn the right to push once you can actually control the movement.