Failure. A concept so powerful it drives human behaviors from cradle to grave. Whether it's an "F" in school or losing the "perfect" job, we learn failure is a mark of shame to be avoided at all costs. But without failure, many life-changing products would never have been invented. From penicillin to the implantable pacemaker, potato chips to Post-It notes, professional failure has been instrumental in improving our lives -- or at least easier to remember the milk.