Two sides of the same coin by Johnzo

I've been thinking about how the MIB cannot kill Jacob and possibly vice-versa. Let's think for a moment that they are inherently the same person, possibly split into two identities, possibly because of time traveling side effects. Same person, just two different bodies and minds. Say that one rule is you cannot kill yourself and/or the island won't let you kill yourself no matter how hard you try. This explains why MIB couldn't kill Jacob.

Now here's the next part. Maybe MIB is trapped because Jacob is older than him in the sense that Jacob has time traveled to a later period of time on the island. If we know Jacob has been living in a later time period on the island, that means that MIB cannot leave the island until the last moment Jacob has existed in the future. For example, say they both were born in 1800, but Jacob time traveled to 2010 and lived there for an extended period of time. That means that if MIB wanted to kill Jacob, he would have to wait until 2010, because you cannot kill someone in 2009 if its a fact they existed in 2010.

Now that Jacob is dead, MIB's future is open, assuming Jacob hadn't traveled much further into the future. If they are two sides of the same coin, and Jacob is always living in the future, it makes sense why the death of Jacob would free MIB.