If you're a parent and your kid wants something, common preference finding usually doesn't mean you have a long discussion. Most things kids want are small and immediate, and can be done faster than a big discussion.
If you think it's a good idea, just do it. If you think it's a bad idea, say this:
I'd rather not do that because [short reason]. If you still want me to, then I will.
Optionally, you might say briefly what you could do instead. Especially if it's a bigger issue, rather than a really little one. But only if you think your kid would want to hear it.
This way, there won't be a long discussion. There won't be a big back and forth. This strictly limits how much your disagreement delays your kid getting what he wants. It keeps transaction costs low.
But the kid does get advice. He does find out why the thing he's asking for might not be good. You wouldn't just want to do whatever he asked without sharing your useful knowledge about it. But you don't want to block him from getting what he wants by arguing a lot.
Suppose your kid wants something and you're busy. Don't ask if it'd be ok to wait 20 minutes, and then he says he's not sure, and then you ask if 10 minutes would be ok. Then you're getting into a discussion that takes too long and is too unclear how your kid can get what he wants (now, if necessary).
Instead, say something like this:
I'm busy. Can you wait 20 minutes? Otherwise I'll stop and do it now.
This keeps it simple. You make one short objection. You give the kid some clear and immediate options. He can have what he wants right now with no further discussion. Or if he doesn't mind waiting, then you can finish what you were doing.
It's important to say stuff like this because the kid may prefer your alternative option. Sometimes he won't mind waiting. You wouldn't want to drop what you were doing every single time, even if the kid could have waited half the time. It's better for both of you if he sometimes prefers for you to finish, when it won't be a problem for him. But you also don't want to put a big obstacle between your kid and getting the help he's asking for.
A reason child may prefer to wait is that parental help is a limited resource. The child will benefit by using it efficiently. Interrupting the parent will use up a bit of the parent's energy, and it'll take some extra time to switch tasks and switch back (like to find his place again, and remember the context, if he was reading). In general, parent will be able to help more with other things if he's got fewer demands on him.
In the examples, the parent does a single pushback on what the kid wants. This gives one opportunity for the kid to get new information (parent currently in the middle of something) or criticism (a reason it's a bad idea), and then change his mind. That's good because it allows for improvement, and without it a worse outcome would happen frequently. But multiple pushbacks is frequently too many and burdens the kid. A single pushback is a good amount to use for most everyday events.
If child agrees to wait, he may change his mind, or parent may be busy longer than expected. If child comes back and asks a second time, parent should help immediately. Don't repeat that you're busy or make a second request for child to wait. This keeps it to a single pushback for the issue and makes it safer for child to agree to wait.
Every single pushback or back-and-forth or layer of negotiation is a big deal. People don't have enough respect for how much that needs to be minimized. You can discuss back and forth more when your kid wants to, that's fine when everyone's interested in doing it. But there are going to be a lot of times when he doesn't want to.
Notice how these statements are structured to limit the amount of times the parent and kid go back and forth talking. Kid makes request. Parent does one pushback. Kid chooses to either get his request immediately or accept the pushback. That's it. And the parent clearly states these options to the kid, so he knows he can get what he wants, right now, without any further arguing or pushback. The kid does not have to argue back against the parent. And the kid does not have to have a discussion where the parent speaks several times.
The kid is welcome to ask for a larger discussion if he wants. He might ask if there's any other options, or can the parent explain more. He might ask a question about what the parent said. He should be told, in general, that he has options like that. But don't state those options every time. Stating two options is enough for small everyday events – with one option being the kid's initial preference, and the other being the parent's alternative suggestion.
Parents should get good at making appealing alternative suggestions without having to question and argue with the kid for 10 minutes and then have 5 tries at telling him alternatives. Parent needs to get skillful at this to reduce the burden on the kid.
It's important the parent be happy. So parents should also get good at being happy to help their kid. And get good at being interruptible during most activities. And get good at thinking, "I got to say why I thought it wasn't the best idea. I got to express myself. But my kid still disagreed, so it must be important to him, and I better help."
It's important for the parent to remember that if he negotiated with his kid more, it'd interrupt what he was doing anyway. Or if he argued with his kid more about a decision (e.g. whether kid can stay up late tonight), then he's making it harder for the kid to be his own person. Parents need to stop having agendas they are trying to push on their kids, and instead understand their role as helpers. Parents should only pushback more than once if they really, truly think the kid will regard it as helpful and thank them for it (right now, not later).
This will not solve every problem parents have. If kid wants a yacht (which is unusual), parent can't just say "I think that's too expensive, but if you still want it I'll buy you one." But it will help with a lot of small interactions.
If you don't know dozens of concrete, practical parenting interactions like this, you could be a much better parent.
And if you didn't know this one, try to understand that you still don't know it after you read this post. It's not going to just instantly work in your life. You might be able to immediately do something better than you used to do. But you're not done yet. Remember it, try it out, see what goes wrong, ask some questions about it, make some adjustments, etc. Then you'll form a real, thorough understanding.
You can find out ideas like this by discussing your parenting and getting tips from other people. And other people can point out some problems you didn't see with your parenting (and you can point out some of theirs, since you'll have different perspectives). And you can ask for ideas like this to help with your life, instead of passively waiting for me to post them unprompted. Take some initiative to get better parenting knowledge!
If you already have some really useful parenting knowledge like this, share it. Other people need it and can offer you refinements. If you have none, your parenting could be way better! Start actively seeking out more knowledge right away!