Not to speak for Cass but I think he's talking about the ingrained patterns of a habitual mind in relationship to an illness.
But I want to look deeper into this side of the coin. Some people do not want to give up an illness whether, psychological or physical, because it serves a purpose. These people are the poster children of neurotic behavior. The psychological payoff for retaining an illness is greater than curing the illness and facing life on its own terms.
I'll use agoraphobia as an example because it is simple. This will show that retaining an illness has a goal or a purpose that fulfills a psychological desire. Albeit at a neurotic one. So we have a person that can't or won't leave the house and I will overlay it with the four goals of misbehavior( or neurotic behavior.)
The people in his life have to come to him to serve his daily needs. Does he most value the attention he's getting from others? Does he value the power over everyone to manipulate them into his service? Is he getting revenge against others by unnecessarily inconveniencing them. Or is this a display of inadequacy? ( at this point it is probably full-blown depression and an almost infantile psychological outlook.)
I see no reason why a legitimate demonic oppression can't be used much the same way.
Bear in mind that this is not a hard-and-fast rule, one-size-fits-all approach. The neurotic is probably miserable. And consciously wants to get better. But unconsciously that fast-moving train has a goal and a purpose - a destination.
