The Piast family has had a rough time of it lately. Władysław is an imperfect ruler (to say the least), Sieciech is undermining the entire dynasty, and the issue of succession is really making a mess of things.
Yet, of the entire cast I feel most sorry for Zbigniew. He didn't ask to be shipped off to a convent, put in charge of a rebellion, and cast aside like an unwanted child. Yet he was.