I agree with Lost. A rupture tears at the very fabric of the therapy relationship and damages the trust that has been built up. It can even feel like a betrayal. Sometimes the rupture can be triggered by the transference or counter transference (client's feelings towards T or vice versa). I've experienced it with current T and it's devastating. It can take a long time and a lot of work to repair and sometimes it doesn't get repaired at all, especially if the T can't own their role in it and/or becomes defensive. It's far beyond a disagreement which is simply when therapist and client are expressing conflicting opinions over something. Disagreements can be horribly upsetting and unsettling but rarely rupture the relationship. Disagreements are actually healthy as a client can and should feel able to voice their views to T.