“I haven't failed! I’ve discovered a thousand ways that won’t work!” – Edison

Failure is the declaration that one will no longer pursue the thing they were trying to accomplish.

If the byproduct of experiments isn't useful and you can't tell how close you might be to a solution, it may not be a failure because you are refusing to give up, but not exactly success either.

Actually the perfect definition of this is obsession. Not exactly healthy but often a necessity.