Here is a great question from a very knowledgeable reader:
Therapy does not solve everything. Some problems are insurmountable. When do you decide as a therapist that the cost-benefit is not worth it? Of course, the couple has to decide that. But if one person wants to work on it and the other doesn't. When is enough, enough? What criteria are used in that case to say something isn't working. Some couples give up too soon. Some stay too long. Some are locked into staying even when miserable.