There is no such thing as the blank slate; like saying children are born as a blank slate! Every time your T engages in a conversation with you, asks you a question, fidgets, is late, thanks you for your check as you hand it to her, you are learning what sort of person she is.

However, what the blank slate affords, that is valuable is a "triangle" made of our projections/transference and T, and ourselves. We can "see" what we are doing up on the slate space because it isn't crowded with "actual" versus imagined thoughts and feelings about T and her life and views; it's all about us and that is what therapy is for! Imagine it like you would two professors with a blackboard discussing their latest theory. They "know" one another but it's the theory, what's going on on the blackboard they want to focus on at this time.