Well, in a spiritual sense there perhaps are no failures, just learning experiences...but it depends on the context. I can see both pros and cons to the idea. If a sense of "failure" induces guilt or self-hatred in a person, that is not productive. If it induces a strong desire in the person to do better next time, that is great.

Hitler's attack on Russia was not "deferred success"...LOL! No, what is was, was this: a mistake. A HUGE, GIANT MISTAKE.

Don't confuse mistakes with failures to reach desirable goals. Mistakes are not worth repeating. Incomplete attempts in a useful direction are worth repeating and improving upon.