Explore and understand how the client currently relates to other people

Mikulincer & Shaver state that one of the therapy tasks of a good therapist is to "explore and understand how the client currently relates to other people." Sometimes this results in the therapist helping the client "become aware of previously unrecognizable biases and failed relational strategies." How does a therapist do this while still maintaining the role of a "secure base" for the client - and environment in which the client feels safe exploring?