Freud illustrated the concept with the example of a person beginning a train of thought and then pausing for a moment before continuing to a different subject. His theory stated that by inserting an interval the person was "letting it be understood symbolically that he will not allow his thoughts about that impression or activity to come into associative contact with other thoughts." As a defense against harmful thoughts, isolation prevents the self from allowing these cognitions to become recurrent and possibly damaging to the self-concept.