I feel like a strong hook should give you the choice between
one of the three options:
- Convert it into a reusable weak hook
- Prevent hostile actions
- Use for things that you cannot use a weak hook for.
- Instead of having two categories like "Weak" and "Strong", hooks should have a strength rating from 0 to 100. This rating will be dynamic and will be calculated depending on:
- Source of hook (knows about murder secret, did them a favor etc.)
- Target's traits
- Target's rank
- Target's lifestyle perks
- Blackmailer's traits
- Blackmailer's rank
- Blackmailer's lifestyle perks
- Whenever trying to use the hook, the target will weigh the strength of the hook against reasons that would incline him to not accept the hook e.g. if the blackmailer is asking the target to murder their own child.
- If the hook's strength is bigger than the target's reluctance, they will accept. Otherwise they will refuse and the blackmailer will be free to reveal their secret.
Similarly I want the system to be expanded a little so that "threats" are a thing. Instead of using a hook, perhaps I can threaten someone weaker than me that I will kill their heir / abduct their daughter etc. if they don't comply with my demands. The target will then weigh the strength of my threat against many other factors and decide what to do.
I've been banging my head against the wall trying to think of a plausible solution to all the problems with hooks pretty much since I read the DD, but I think these two ideas combined will work wonders. Although note that I have no idea if it's actually possible in the game and how taxing it will be on performance. I also understand that it's kind of nuts from a roleplay perspective, but I think it strikes the right balance between being a somewhat uncommon method of ordering others around and not being too frustrating when used against you.
So you have a hook on someone with a strength rating of X. This person's acceptance to join your plot is -Y. So you use a hook and Y+1 is added to your acceptance, resulting in a total +1, which makes that person accept. The same Y+1 is subtracted from your hook strength and it's now X-Y-1! If it's enough for you to coerce that person into more plots, you can reuse it, but at some point it's going to get too low for there to be anything left to do. So if there's that one courtier just short of hopping onto your murder spree even after a bribe, you can use a hook on him repeatedly, chipping away tiny bits of its strength each time, but for a loyal, moral and capable spymaster, who will certainly doom your scheme unless he joins it, you might have to use everything you have to get him onboard. This creates a situation where it's beneficial to both bribe and blackmail/indebt/call in a favour with someone, as the closer their acceptance is to 0, the more you can reuse the hook.
I also really like the potential narrative of "Accept this gift as a sign of our friendship. Come now, I know you want us to be friends! After all, friends do keep each other's secrets... And now that I've solved your financial issues, I expect you to help your new friend with a small problem."
As for using a hook to prevent hostile actions, it could be a toggle, which makes the hook's strength decrease with time as long as the non-aggression pact is in force. The decrease could be based on relative power, (if that's too difficult to code, then just add/subtract points based on rank and number of titles held by each side, number of vassals, maybe if one side is a powerful vassal), but also on available CBs, so while you can make your brother reconsider pressing his claims for everything you have, it might not be for long. I think it should also be influenced or stopped entirely by conditions prohibiting certain or all hostile actions, such as disallowed internal wars, councillors not being able to join factions, active realm peace or both parties being on the same side in a war, (I don't actually remember which of that is in CK3 and not just in CK2, but you get the idea).
As a side note, I feel like if this method of using hooks is introduced, there'd be no reason to cap strength at 100, as it's tied to other factors.
This same system could probably be used for threats, but I just don't know how to make them make sense. If you can gain hooks on people by threatening them, you can wind up with situations like "If you don't want me to kill your son, help me kill all his children" or "If you don't help me kill the last in line to your empire before my son, I'll declare war on you and take a single county." And even if you're threatened and refuse, you now know that one of your relatives is in danger. What's more, it might make sense for you to be able to declare that so-and-so admitted to wanting to murder someone. After that, most potential agents will probably get -10 or whatever relations and some of them might not accept it anymore. "Oh, you wanted to kill that guy? Man, that's bad. I mean, if you'd asked me yesterday, I'd probably have agreed, but now? Sorry, I only condone undiscovered murder."