"We are the causes of our own suffering" by curt michaels

My theory is this:

Without realising, the man in black has already removed the smoke monster from the equation in the past, when he killed his mother (smokey). He plunged the dagger through her chest, without her speaking. Much like Dogens advice to Sayid when sending him to kill Flocke.

Perhaps Jacobs whole purpose in "guarding the island" is simply to protect the source, but what did Jacob do, he sent his brother down the stream, into the light, making everything, quite simply go dark. Enter smokey.Hence Jacob ironically being the cause of his own suffering. The exact words we see used in the Room 23 video.

Another ironic part of all this, Mother actually wanted man in black to be the one guarding the source, and he ends up being the one sacrificed to it.

Desmonds "sacrifice" will be to enter the source, the islands heart, and turn the light, back on, once and for all.