The answer is resistance. It is loosely defined as a client's unwillingness to discuss a particular topic in therapy.
There are uncountable reasons why clients can be resistant within a therapeutic relationship. People of all cultures, natures, and personalities visit psychologists, each with their own reasons for entering therapy. Some people may be ordered or referred by a third party to enter therapy. Since they are not there of their own will, these clients are often unwilling to be there and can show very obvious struggle to the process. Regardless, many clients show some sort of resistance to the emotional pain that change demands. Clients can be unwilling and opposed to change even if it is what they desire, as change can be difficult, emotionally painful, or scary.