Hope must be a part of the SI, and I'm sure it usually serves a useful function. Even when dealing with something that has no chance of improving, like a chronic incurable illness that is only going to get worse, hope has a funny way of popping up and distracting you from thinking about the harsh reality of the future.
It can produce moments of blissful ignorance, or coping. In a moment of being distracted from an awful situation, one forgets how unbearable it is until the focus inevitably shifts back.
OK, a lot of the time things may seem more hopeless than they really are, or it can be hard to determine the value of hope and likelihood of imrovement... But when the situation is truly inescapable, hope acts like a psychological opioid that temporarily masks a growing pain and eventually becomes ineffective. This can leave you in even more pain due to a delay in taking actions.
In the realm of ctb, especially with debilitating disease or illness- It takes considerable strength and effort for a person to accept when this hope is certainly a delusion, and might be preventing them from taking the necessary steps to arrange for a more acceptable/painless outcome.