Been thinking about Shantanu and Bhishma and I love the juxtaposition of their actions.
In breaking his promise to Ganga, Shantanu allows Bhishma to live. The price of saving his son was losing his wife. But she didn't leave him without hope altogether. It is both a triumph (finally choosing life) and a defeat of sorts. He did the right thing in breaking his vow.
Meanwhile, you have Bhishma, who in keeping his oath, allows his father to live happily with Satyavati. He does everything right by the "rules" of dharma. It's glorious and he is honored for it. But in that same act, he sets into motion everything that breaks the dynasty. When he refuses to break his vow to father children on Ambika/Ambalika (that whole sequence angers me for no reason but more on that later), he further dooms the very dynasty he swore to protect.
A broken oath in the face of changing circumstances: that was what Shantanu managed to do, and Bhishma could not.
Only if you'd learned from your father, Bhishma.