I have noticed there is a lot to do with folks putting on shoes. Especially Locke, and Christian. If you notice, Christian arrives with white shoes, he must have had his shoes changed at some point before I believe Jack changed his shoes if my memory serves me correctly.
After his father's death, Jack Shephard felt that the corpse did not need new shoes, and instead gave his father an old pair of white tennis shoes that he had. Jack later attributed this to the fact that he didn't think his father was worth a new pair of shoes. Christian wore these shoes while in his coffin aboard Oceanic Flight 815.
So Jack didn't think his father was worthy of new shoes huh? Why - because he didn't understand his fathers viewpoint, he wasn't emotionally mature enough to get this, because he hadn't seen things from his fathers point of view.
Jack had no faith in his father, he lost his faith. So he deemed him unworthy of shoes.
Should his old man have been wearing the black shoes? Would a different outcome have happened?
Obviously, shoes are of importance here. If he had his black shoes on at his time of crashing, would he have become MIB? Something about the 'proxy' replaces their previous iteration or allows MIB to reincarnate his essence into them. But because Christian was not wearing the right shoes, I believe he was unable to become the proxy...
Did Jacob ensure this by causing Jack to deem his father not worthy and make sure he didn't give him the right shoes so that he could never make the loophole earlier than expected?
Anyone notice, as well, that Locke had no shoes on when he arrived on the main island via the jetty after riding there with Ben on the boat?
Maybe shoes are more important than we think, and are the binding force to replication/proxy/substitution on the island. And now MIB has become FLocke, then perhaps the previous iteration of Locke, is free of the curse that bound him.
I can't wait for season six god damn it!!