korien_dec13“When he makes a promise, he never fails to fulfill it.”

If something or someone never fails to do something, it means they absolutely always do it. After all, if they didn’t do it one time, they would have failed to do it.

You can also say “It never fails” as an expression of frustration. If it rains and you’ve forgotten your umbrella, you can say “It never fails” to mean “It always rains when I forget my umbrella.” Maybe it’s a little exaggerated, though!