For one thing, it is very commonly known that people actively lie to their therapists, not to mention not being able to get into things that are difficult. Therapy is a process so it will change like anything else, even more so because it is designed to be flexible with whatever "truth" is present. And therapists all know this and do not keep tabs on white lies or avoidances. They are willing to accept whatever comes to them and respond to that, knowing full well that people are all different and have different feelings about how revealing they want to be.

It is also quite well known that shame or feelings that you might be judged or even somehow rejected by saying something to a therapist is also part of the process. If it is bothering you, and you want relief by saying something, then don't worry about what the therapist might think. You are there not to make friends or impress anyone. You are there to tell your subjective experiences and the closer you get to the truth of them the better off you will be. Plus I really doubt that a therapist hasn't heard a great deal of all kinds of things so will probably not be surprised or reactive as you might think. Holding yourself back when you actually feel it would not be good for you could be addressed on its own in a session. You might find that it comes from certain things that you are not completely aware of and that might help you without actually going into the details. Then you can decide after such things are worked out.

Therapy is also limited by time constraints, so that the full truth could never really be explored in detail. Some things have to be left out. It's just the practical reality of time and the constraints of the relationship, where unlike a friendship or something else, you simply can't just have the therapist available all the time. Instead each session has to take up an issue or two or three and that's about all. The therapist isn't a magician and isn't a judge. The therapist is there to listen and understanding, use whatever training and approaches learned to help you. And people don't go into the profession unless they want to help. It doesn't pay like other professions and is quite demanding of the person. So therapists are generally there because they've made certain choices that are all about helping others and not about their own needs. Put the needs of your therapist aside. The relationship is important, but it is for you, not the therapist, so in a sense is unlike all other relationships.