I always end up lying to psychologists, even if I don't intend to.
I rationalize by saying I'm just giving them what they want, but I think the reason is more complex.
Part of it is cynicism concerning psychologists, part of it is after years of masking it's become second nature, part of it is vanity I want to make my life a little more exciting than it really is, and part of it is a life long love of story telling.
But, I think, the largest part is I'm simply not 100% sure of my reasons for transitioning, and one has to fill up the allotted time.