What a failed Trident test can still prove

How should the failed Trident test be understood?

The submarine test succeeded, the aging missile failed, and the failure provides evidence that can be used to correct the system.

The submarine and its launch systems performed their part, while the missile used for testing was drawn from a stock with a finite service life. A reported failure is useful when it exposes a correctable problem, and governments normally avoid detailed public comment on strategic-deterrent operations.