Interpretation

But before he had even finished the work, he knew that it was a failure.

There's no context. It's just one of examples from a grammar book (no interpretations). It frustrates me. I don't get what that means. Could I supposedly interpret it as this: He had conjectured that it would be a failure in the first place. Nevertheless He had kept on proceeding to business. (Above all, Is that grammatical from the beginning? "Past" can antecede "past perfect" as in time? Please help me understand it. I'm thoroughly confused.)