I am a first time reader of The Dark Tower series and am currently on book 2. I was wondering about the doors. How come people can sometimes see them and sometimes they can't. I have just read the bit where Jack Andolini gets drawn in, but before he did he could see the door. Why couldn't he see it before? And what is meant by Roland "coming forward"? I assume it means taking control over Eddie's body? But not sure.

If the answer to my questions are answered later on in the book(s) then please just say no comment.

Thanks