This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Carpe Jugulum
Mightily Oates burns his holy book to save a life. Just very powerfully written.
Made all the more powerful because he does it with little hesitation, in a manner that says, "I can't think of a better use for this."
Granny Weatherwax is called to help at a difficult birth when the midwife cannot cope. She ends up having to make a decision whether to save the child's life or the mother's. After she makes her choice the midwife says she should have asked the father/husband to make the decision. Granny's answer: "What has he ever done to me that I should hurt him so?"
Simply seeing Granny Weatherwax of all people suffering debilitating weakness is heart-wrenching. Granny's personal plot is about how, after years of having to make hard decisions and being, as she herself admits, judgmental, opinionated, stubborn and generally unlikable, she begins to worry about whether or not she really is a good person. When she thinks that she's been snubbed from the christening of Magrat's own daughter, she feels like her acerbic attitude has pushed away one of her only friends, leaving her so lonely and sad she decides to just pack herself off to die. She's doubting everything about herself, including whether or not she's done anything actually good in her life, and it's an incredibly depressing moment of vulnerability in one of the Disc's most ordinarily indefatigable characters.
It gets worse; back in Witches Abroad, it was established that Granny firmly believes that she was always supposed to be the Bad Witch character, except that her sister Lily became an Obliviously Evil Bad Witch instead and so karma demanded she take up the Good Witch character instead. And the events that kickstart this whole mess? They're straight out of an old fairytale, where a witch (or evil fairy) is not invited to a christening and so decides to seek revenge on the family. And as much as Granny hates to admit it, deep down, she's got a fondness for kids. In addition to her own emotional turmoil, she packs herself off to the gnarly ground because she's scared that Narrative is going to force her to embrace the child-harming bad witch role, and she's not going to have that.