For context

How would you notice it isn't holding?

The question sounds pessimistic and is the opposite.

Anyone who can answer it can decide. Anyone who cannot keeps optimising and finds out too late.

In two mandates this was exactly the gap. In one there was a number without a denominator: 89 per cent complete, and nobody could say of what. In the other there was no number at all: a nationwide rollout was imminent, and nobody could name the value at which you stop it.

Both cases are written up, with the figures and with what I am not claiming.