“How can you tell whether it is a demon or just the flesh?” My answer to that question is that it is almost always both, at least to some extent. A demon charged with harassing me would be a fool to see me having an emotional or mental problem and not try to complicate it. It is true that I am “lured and enticed,” as the RSV puts it, “by [my] own desire” (James 1:14). The flesh is always involved. But Satan is not so foolish as not to take advantage of the struggle going on within me. So I need to be ready to deal with my part of it, but I also need to be ready to deal with the enemy.
Timothy M. Warner, Spiritual Warfare, page 100.