Can you talk more about this? Why grudges exist, what happens if a dwarf has cause to declare a grudge and does not, what happens before the grudge is fulfilled if it's neglected. You've represented it before during Karak Ungor, as they were striking them out from the list of grudges, curious to hear more
I mean...'why grudges exist' is sorta just...because they do? Dwarfs when they feel they are wronged can and will declare a Grudge. It's a part of their psychology and society, to try and gain recompense through one measure or another from being wronged.
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When I were but a lad, my father, the King, taught me three things: Never accept a gift from an Elf, never trust gold that glistens in the darkness, never forget a grudge. On his deathbed I swore to uphold those values to me own dying day, and Grungni willing, I will."
—King Alrik Ranulfsson of Karak Hirn.
Dwarfs have a rigid and unyielding sense of honour, which is centred around oaths or a promise. A promise does not die with an oath-maker, nor does treachery die with an oath-breaker. A Dwarf will be bound to an unfulfilled promise made by an ancestor, and will commit themselves to their fulfilment. Likewise, they will look to the descendants of oathbreakers for recompense. Serious breaches of faith against the Dwarfs are recorded in the Book of Grudges. This massive tome is kept in Karaz-a-Karak, the capital of the old Dwarf Empire, and constitutes something of a chronicle of Dwarf history. < from one of the dwarf infobooks, 1ED in fact. So it's been part of the setting for a long time, nothing to contradict it.
There's plenty to not take precisely from Total War Warhammer, but the Grudge system is reasonably good, including the old one. Specifically, to let a Grudge linger is a shame - not just on your character and being, but on your family, your Clan, your Guild, your Hold, etc. Sometimes, Grudges cannot be struck out in a timely manner, like you could die of old age as a dwarf, and the Grudge will still remain and it is your descendants responsibility to take it up and try their best to fulfill it. Sometimes, you can give reasonable warning, like with the missing gold/copper for that one Castle thing. Other times, you killed my father, I need to ensure you die. Or if you die from old age, your kids have to die, and if I die before I can kill you or your kids, then my kids have to do it.
It's endemic to them. Remember, while they might share a lot of things, there are just some things that show the dwarfs and elves as non-human. They can have very human reactions, or from their perspective, many humans can have very dwarf-like reactions, or very elf-like perspectives and behavior. But they aren't. Allies. Yes. Friends, yes. Lovers? Eh...perhaps, in a few weird cases. But they aren't human. Dwarfs are generally expected to be outraged over wrongs, furious, demanding, vehement about getting them solved, but it also means that more Grudges fill their Books than can be struck out in a reasonable manner. Sometimes it can be a petty grudge, sometimes not. You spilled my beer is not necessarily a Grudging, but you spilled my great grandfather's tankard onto the ground and spat on it with your dirty foul mouth and kicked it away after you slipped on the ground and landed so hard that your barely held in diarrea sprayed all over it and then insulted me over getting in your way? That's a Grudge, probably, even if it might not be a killing Grudge. There are multiple ways to 'finish' a Grudge, killing is just the most loud of them. Weregild is also a thing, depending on what the Grudge was about and the dwarf in question.
Sometimes, a dwarf might consider a Grudge satisfactorily dealt with, and even if in the future, some of his children might look back and think, he should have done more/gotten more, the ancestor veneration and elder worship of their culture means that they'll most likely not actually denigrate or spew about it. Because he was the elder, the ancestor, and they're not going to criticize what he did or didn't do.
It doesn't have to happen, though.
IC, it was considered a very big deal when after Thorgrim and Tyrion both worked together to save the Everqueen's daughter, and Tyrion insulted them at the battle's conclusion and was being a real jerk about things, the longbeards and clan leaders with Thorgrim went 'GRUDGE GRUDGE GRUDGE GRUDGE' because he insulted them!
Did he attack them, no, did he kill some of them, no, he just criticized them a lot because he felt they were too slow and that's why the effort went bad. And plenty of the leading dwarf cultural figures at the time said 'PUT HIM IN THE BOOK'. Now, was the 'striking out' clause for that Grudge in particular going to be bloodletting? Not necessarily, but possible. He could have apologized 'sufficiently' enough, and that might have solved it as well. But Thorgrim said 'no, not this time' and shocked all of them. And they went on their way, grumbling, but without a Grudge causing even worse strained issues later down the line.
I'm a little scattered at the moment, so this isn't super comprehensive or complete, but hope this is something!