The fact that the scale in the cave was "balanced" with black and white seems to support this theory. I also think that the opposites are always in a battle, in you, as to how you will respond to a situation. If you believe you are destined to "be a killer" as Sayid thinks, then that becomes a self fulfilling prophecy. Our beloved characters all seem to carry a "label" with them, Jack - doesn't have what it takes, Hurley - unlucky, Ben - liar, Sawyer - con man. How will that internal battle play out and can they shake that label, do they want to or have they conceded that they cannot change - that is the point. What will we do to get our wish - Sawyer seems to be willing to go along with FLocke to get off the island, for example. Will we compromise our values etc? How many times do we wish, if we could go back and change this event, it would all be better. Does the what happened, happened and TT play on this desire to show that you can't change what you did but you can certainly alter your present state, if you choose?