Does evil exist for good, does good exist for evil, or do both good and evil exist for a common purpose?

Which is ultimately for the purpose of the other: good or evil? In stead do each have a mutual, common interest? In most faiths evil is the antagonist and good is the protagonist. Take Christianity for instance. The bible is full of heroes for righteousness and good. Joesph's bothers did evil unto him, but Joseph became great in the land of Egypt as a result. However, Joseph's high standing might not have occurred but for the evil act of his brothers. Were Joseph's brother's purpose for evil to uplift good for generations with this story of triumph, faith and hope? If evil had not influenced creation, would good would merely exist on its own merit, unhampered for eternity? For every great accomplishment of good, there is usually some aspect of evil that had or has to be restricted, overcome, shielded, refined or somehow domesticated for the civilization and goodness of man. Man himself serves his interests through both acts of good and evil. Even without regard for faith, change among civilizations is the product of both good and evil whatever the origins of this dual component of man's intellect and prowess. Maybe evil is allowed or permitted for the accomplishment of good. Let's all truly hope that good is meant to travail, but even then hell, Hades is suppose to eventually be composed of all evil.