What causes the doors? Roland makes a guess that --
I think that ka definitely exists within the books, and that DT III makes that most clear, but I have a feeling that some folken here will disagree with Roland's interpretation, and others might just be able to conjecture more detail. So, what do you think? How does all of that work?... On one end, my ka. On the other, that of the man in black -- Walter. The doors were the center, creations of the tension between two opposing destinies. ...
-- DT III The Waste Lands