Therapists are trained to be observant and skilled in picking up cues and patterns in their clients' behavior, body language, and communication. While they may not know everything a client is withholding explicitly, they might sense when something is being held back or when there are gaps in the information being shared.
Many therapists are trained to create a safe and non-judgmental environment to encourage open communication. They might gently inquire about any hesitations or inconsistencies they notice, providing an opportunity for the client to share more deeply or explore any underlying concerns.
However, it's essential to remember that therapists are not mind-readers, and they rely on the information clients choose to share with them. Being honest and open with a therapist is crucial for the therapeutic process to be effective and for clients to receive the best possible support. If there are reasons why a person feels uncomfortable sharing certain things, it can be helpful to discuss these feelings with the therapist to build trust and work through any obstacles in the therapeutic relationship.