Sri Aurobindo
Letters of Sri Aurobindo
13. Opposition of the Hostile Forces
The normal resistance of the lower Nature in human beings and the action of the Hostiles are two quite different things. The former is natural and occurs in everybody; the latter is an 
intervention from the non-human world. But this intervention can come in two forms. (1) They use and press on the lower Nature forces making them resist where they would otherwise be quiescent, making the resistance strong or violent where it would be otherwise slight or moderate, exaggerating its violence when it is violent. There is besides a malignant cleverness, a conscious plan and combination when the Hostiles act on these forces which is not evident in the normal resistance of the forces. (2) They sometimes invade with their own forces. When this happens there is often a temporary possession or at least an irresistible influence which makes the thoughts, feelings, actions of the person abnormal – a black clouding of the brain, a whirl in the vital, all acts as if the person could not help himself and were drawn by an overmastering force. On the other hand instead of a possession there may be only a strong Influence; then the symptoms are less marked, but it is easy for any one acquainted with the ways of these forces to see what has happened. Finally it may be only an attack, not possession or influence; the person then is separate, is not overcome, resists.
There are some who are never touched by the hostile forces.