The more consciousness there is in such a sufferer who in despair wills to be himself, the more his despair intensifies and becomes demonic. It usually originates as follows. A self that in despair wills to be itself is pained in some distress or other that does not allow itself to be taken away from or separated from his concrete self. So now he makes precisely this torment the object of all his passion, and finally it becomes a demonic rage. By now, even if God in heaven and all the angels offered to help him out of it- no, he does not want that, now it is too late. Once he would gladly have given everything to be rid of this agony, but he was kept waiting; now it is too late, now he would rather rage against everything and be the wronged victim of the whole world and of all life, and it is of particular significance to him to make sure that he has his torment on hand and that no one takes it away from him- for then he would not be able to demonstrate and prove to himself that he is right. This eventually becomes such a fixation that for an extremely strange reason he is afraid of eternity, afraid that it will separate him from his, demonically understood, infinite superiority over other men, his justification, demonically understood, for being what he is.
Søren Kierkegaard, The Sickness Unto Death: A Christian Psychological Exposition for Upbuilding and Awakening
demons