In introspection the emphasis is on the thought, the feeling, the emotion, the mood, anger, or anything, and the self is forgotten; in self-remembering the self is remembered and the whole energy is centered on the self, and you just look at the mood, at the situation, at the feeling -- you don't think about it, because in the thinking the look is lost, the purity of the look is lost
Witnessing is a step further ahead. In witnessing, even the self is dropped; only remembering remains. Not that I remember. The "I" is no longer part of witnessing. Just remembering.... Witnessing is a witnessing of the self. Self-remembering is the beginning; witnessing is the end. But when you look at the mind, by and by, the mind disappears. When the mind disappears and there is void, then a new step can be taken: now, you look at yourself.
In witnessing there is no self. You look at the anger, but when you look at yourself, you are no longer you: just a vast, infinite, unbound witnessing. Just consciousness -- infinite and vast, but with no crystallization.
Gurdjieff worked his whole life on the method of self-remembering because in the West to introduce witnessing would have been almost impossible, because the West has been living with introspection. Witnessing can be introduced only when self-remembering is settled; before it, it cannot be introduced. To talk about it before the ripeness of self-remembering will not reach anywhere; it will be useless.
In the East we have used all the three: introspection was for very ordinary religious people, those who don't want to go deep.
Those who want to go deep, for them, self-remembering; and those who want to go so deep that they disappear in the depth, for them, witnessing. Witnessing is the last. Beyond that, nothing exists.
You cannot be a witness to the witness -- because that too will be witnessing. So beyond witnessing there is no possibility to go: you have come to the very end. The end of the world is witnessing.
Move from introspection to self-remembering, and from self-remembering hope some day to move to witnessing.