In this world, there is no absolute good, no absolute evil," the man said. "Good and evil are not fixed, stable entities but are continually trading places. A good may be transformed into an evil in the next second. And vice versa. Such was teh way of the world that Dostoevksy depicted in The Brothers Karamazov. The most important thing is to maintain the balance between the constantly moving good and evil. If you lean too much in either direction, it becomes difficult to maintain actual morals. Indeed, balance itself is the good.
