It completely depends on the therapist you choose. Most therapists are respectful of the client's boundaries and don't "force" them to discuss an issue they are uncomfortable discussing at that time. And I think it's very wise and insightful to approach therapy to help you with specific issues, such as X, Y and Z. It means you can have specific goals and if the therapist wants to talk about issues A or B, you can say, "Well, maybe someday I would too, but I really wanted my therapy here with you to focus on issues X, Y and Z." If the therapist pushes, you can push back! You can also decide if a therapist is working or not for you and if not, fire them and find another that is going to work the way you want, on the issues you want.

You always have to remember -- you're the customer in the therapist/client relationship. If you're not getting what you want or need from the relationship, you can move on to find a therapist you do get those sorts of things.

Good luck!
DocJohn