Why Is This Client Different From All Other Clients?

Yes, the title is meant to evoke the well known Passover saying, "Why is this night different from all other nights?"  It came to mind when I was recently working with an adversary on a matter when I called to his attention the fact that his client had reneged on her own prior proposals that my client had already accepted.  Generally speaking, reneging on an agreed upon proposal is unreasonable, if not bad faith misconduct.  Reneging on one's own prior proposals is even worse.  When I challenged the adversary as to the reasonableness of his client's conduct, his response was, "I'm not going to stop this client from doing what she wants to do."  In other words, despite acknowledging his client's own wrongdoing, he was facilitating her behavior by treating her as a client that is "different from all other clients."