I was wondering about this a lot in my own therapy but also from things I read here.
How honest are you really with your therapist about how you really feel or what has happened in your life? Is your honesty sometimes compromised by fear of how the therapist might react? Do you wish you could be more honest with your therapist?
And a bit of a provocative question, but one that surely is important...
Have you ever exaggerated an event or a feeling in the hope to get more empathy, care, love, attention, hugs etc?
And does your therapist sometimes call you on something that doesn't seem right?

In my own therapy experience, I was very honest from the start - about what I want, what I don't want, what I need and don't need.. And I was very open about what happened (and is happening) to me.
But many times I held back and a couple of times told half truths. For example I told her about an event that happened but I left out the most important piece of information and for two sessions we talked about this with only the knowledge I gave her - and I felt horrible because although I could talk through things, I really really wanted her to know the whole truth.
The third session about this topic she said: "Something seems to be on your mind and I think you haven't told me me everything about this event and I want to reassure you that you can be absolutely honest with me. It won't change my feeling towards you and I can promise that." Only then I told her the whole truth and it has helped me tremendously and since then I feel I can't help but tell her everything in all honesty, even if in my mind I want to leave out things.