I usually say I am not going to answer rather than I don't know unless I really don't know. And then that is what I say. Sometimes a person really does not know just off the top. I don't think it is always avoiding something. There are times when I will say I don't know but will think about it. Or even that I don't know and don't care unless the therapist wants to explain how it would be useful to me so that I might decide it could be useful to think about it.