When people don't agree about how to cooperate, coordinate or get along, they may try problem solving. If problem solving fails or someone declines to try problem solving, then typically they should leave each other alone on that issue. If the issue is big enough, there are multiple disputes, or someone wants to, then they can leave each other alone entirely.
If there are obligations involved, like a contract, people should commonly either minimally follow the obligations or figure out a way to end the obligations early. If the obligations have only small importance or a weak level of commitment, then they should often just be dropped.
What does it mean to leave each other alone? This is determined by cultural norms. Society decides what people leaving each other alone is, or respecting the rights of others, or acting peacefully, etc. These things can change over time. Political philosophers can develop theories about how these things should work and sometimes influence society.
Our society says leaving people alone means respecting their rights and keeping to yourself. Don't use violence, violate property rights, break laws, break contracts, or commit fraud. Focus on your own life, your own actions, your own property, and your own voluntary interactions with others for mutual benefit. When a potential interaction lacks mutual consent then it shouldn't happen. There are tricky cases, like noise made on your own property or in public may carry onto someone else's property, and society has some ideas (which all adults should have some familiarity with) about what is too loud during the day or at night at what kind of location (it's different at a residential neighborhood or a factory with a night shift).
If you believe someone refuses to leave you alone, what should you do? If it's a minor issue, ignore it. If communication seems potentially productive, you can tell them your concern. If it's a big issue, you can talk to the police or a lawyer (for most disputes, which don't involve serious crimes, you should communicate before taking this step, even if you doubt it will work). Instead of vigilante justice, people can use independent third parties to make judgments about conflicts. Why? Because you might be mistaken, the other guy might be mistaken, you might both be biased, and society doesn't trust either of you to decide who is right or what the right outcome for the conflict is.
If your conflict is with a coworker, you can talk to them about it, talk to your manager or your human resources department about it, ignore it, transfer to another department or change jobs. If your conflict is with a spouse, you could talk with them about it, ignore it, talk to a couples therapist about it, or get a divorce. If the conflict is with a neighbor, you could communicate about it, ignore it, talk to an authority (police, lawyer, court, landlord, home owner's association), or move. The pattern here is you can try to communicate and do problem solving, ignore the issue, talk to a third party, or separate from the person you're in conflict with. In each case, taking matters into your own hands and directly fighting with the person is generally unacceptable.
It may feel unfair that a person has taken aggressive actions against you but you are not supposed to fight back. What is the reasoning for this? In many cases, the situation is symmetric: he thinks that you've been aggressive towards him while he's done nothing wrong. If everyone who thought someone else was being aggressive started fighting with them on purpose, that would lead to a lot of fighting and escalation. People would pick fights over misunderstandings or after they themselves did something wrong.
Note that fighting back in non-violent ways can be socially acceptable, like using passive aggressive comments, gossip, or office politics. That's somewhat discouraged but also widespread, normal and often allowed. In general, you can fight back using actions like gossip that would be socially acceptable even if you weren't a victim and didn't have defense as a justification. But you shouldn't fight back with actions like punching that are unacceptable in general. There are special exceptions like you're allowed to punch to defend yourself from a home invader because there isn't time to wait for the police to come.
Parenting
Parent and child can't just leave each other alone so there's a harder case there. Leaving each other alone in other cases can be difficult too, e.g. people don't want to change jobs, homes or spouses to avoid a conflict.
My former mentor David Deutsch developed a non-coercive parenting philosophy, Taking Children Seriously (TCS), which has errors. TCS says parents and children should do problem solving and seek solutions they're all happy with. They should reach agreement and act with consent. They should use creativity and communication instead of fighting. They should address root causes not just immediate problems. But what if they try really hard and fail to agree about something? As a last resort which should happen rarely, TCS tells parents to defer to their children:
where there is no common preference found, the parent must self-sacrifice ... Occasional failures, or even frequent minor failures, to find solutions, are probably inevitable, and we endorse parental self-sacrifice as the best way of making them less harmful and less frequent.
TCS thought this was a principled stance. I now think it goes against the standard principles that govern other scenarios. If people fail to agree and also fail to leave each other alone, in general they should defer to the judgment of an independent third party who isn't involved in the conflict.
TCS wanted parents to defer to children because parents chose to have children in the first place, which allegedly makes a parent the root cause of the problem. Also, if a parent is being unreasonable then the parent should defer. But if the child is being unreasonable, then TCS says that is due to the bad parenting in the past, so again it is the parent's fault and the child is the innocent victim who should be protected by the parent letting the child have their way.
What would a reasonable, independent third party in our society say about a conflict between a parent and a child? They would first look at the nature of the conflict. Does the conflict involve someone being inappropriately controlling and invasive in someone else's life? For example, if the child is telling the parent to switch careers to be a musician, because the child likes music, that isn't respectful of the parent's autonomy and right to make their own decisions about their own life. If the parent is an accountant and wants to stay an accountant, that's fine. On the other hand, if the parent wants his child to work in a sweat shop, the third party would say that the parent has no right to ask for such a thing and would take the child's side.
What if the conflict involves a legitimate area of mutual concern? Then in general an independent third party would side with the parent. Why? Many reasons. Parents are smarter, wiser, more rational, more knowledgeable, more experienced and more likely to be right. TCS disputes some of this, and I'm also unimpressed by this reasoning because parents are fallible and children are sometimes right.
Good parents tend to do socially acceptable things or persuade their children. So third parties tend to side with them about conflicts because they know what third parties would agree with and are already doing that. If both society and your child disagree with something, and it's your child's business too not your own personal matter, then you generally shouldn't do it.
Also, the parent is responsible for parenting outcomes, and control and decision making authority should be with the person who will be blamed for bad outcomes. Even TCS didn't think responsibility could or should be transferred to children.
Also, the child is a dependent who doesn't know how to run his own life, so it makes sense for the person in charge of making the child's life work out would also need to sometimes make some decisions to achieve that.
Also, sometimes the child wants things the parent doesn't know how to accomplish or even considers impossible. So then how can the parent defer to the child? This comes up less in the other direction because adults generally have a decent understanding of what is possible or realistic. A child might want a pet unicorn, a visit to mars, a birthday party that costs a million dollars, to meet a celebrity, to do something unsafe, or to go to a business that is currently closed (young children may lack a good understanding of time and schedules and may be impatient and want things now).
Parents can ask for unreasonable things that are too invasive too. It's reasonable for a parent to ask a child to spend time on his math homework and ask a child to try, but it's unreasonable for a parent to demand that the child understand math really well and become a top mathematician who does original research. The child doesn't know how to do that, so even if he wants and tries to obey his parent, it still won't work. An independent third party would likely see the issue with demanding great mathematical ability and disagree with the parent.
In general, these points are more relevant for 5 year olds than 15 year olds (and even more relevant for 1 year olds). If your child is 15 and you can't get along with him, maybe you should give him food, housing, transportation and a bit of money for 3 more years without being too pushy or interfering too much. Wanting him to graduate high school and stay away from drugs and crime would be normal but you don't need to micromanage a teenager who is unreceptive. An independent third party is much more likely to tell you to stop trying to control your teenager than your 5 year old.
In general, actually asking an independent third party to make a judgment is uncommon. And asking someone can be unreliable: people's opinions vary so you won't won't necessarily get you an accurate answer about mainstream opinion. And standard opinions can vary by region and sub-culture (e.g. by religion or ethnicity), so there are issues with asking the right type of third party (sometimes you should ask someone who is the same religion as you, but sometimes you ought to follow the mainstream opinion for your city, region or country). These principles for dealing with conflicts are often reasonably easy to use but are sometimes difficult to use.
Most adults know what standard opinions society has and can follow them without actually having a judge, jury, mutual friend or Reddit thread tell them what's normal. Even adults who are angry at each other can often mostly agree about what is socially acceptable without asking anyone else. And adults can often challenge each other when they think someone is getting the mainstream opinion wrong. When dealing with children, adults should double check themselves more than they usually do: ask friends more, do more internet searches, and ask AI chatbots more. Children often can't correct adults effectively, so adults should do more error correction on their own initiative.
Spheres of Legitimate Authority
Society has ideas about what is each person's sphere of legitimate authority where they get to have control and make decisions. Infants have a small sphere of legitimate authority, but it does include some things like infants may get hungry and want to be fed and parents are supposed to listen and feed them (and if a parent didn't do that, an independent third party would side with the infant). As children get older, their sphere of legitimate authority increases. They start owning property which they can make some decisions about. They start being responsible for some things in their life and therefore also getting some decision making authority. They become more familiar with their culture, more knowledgeable about what is acceptable behavior, more able to predict what judgments independent third parties would make, and more able to think like an adult. They get incrementally closer to independence.
When people are in conflict and fail to agree, if the conflict involves someone's sphere of legitimate authority, then the other person should back off. If the conflict involves an area of legitimate mutual concern, then the situation is harder. Parents and their children, especially young children, have a lot of areas of legitimate mutual concern where they need to get along somehow. E.g. if an adult doesn't brush his teeth, that is his business, not your business. But if a child doesn't brush his teeth, that is the parent's business too because the parent will have to pay for the dentist and also because society expects parents to educate their children on how to live a decent life which includes reasonable dental hygiene.
Conclusion
So I think TCS was wrong. "Parent defers to the child" is the wrong answer. "Child defers to the parent" is also wrong: following general principles, they should both defer to an independent third party.
Conflicts between adults tend to get bad when someone is mistaken about what society's mainstream view or purposefully going against it, or when society would actually consider it a complex situation where multiple opinions have a lot of supporters. Parenting can be hard because children often don't know about or ignore society's opinions, so a parent and child are often less able to use cultural norms as a mutually acceptable default answer than two adults are.
What if a cultural norm is mistaken? Should people still defer to it? If they both think it's mistaken, and they can agree about that, then they can do their own thing with mutual consent (as long as they aren't violating anyone else's rights). And even if people sometimes defer to mistaken ideas, overall progress and error correction remain possible. Cultural norms can improve over time. Anyone may work to try to improve them. I don't think we currently have a great system for improving cultural norms or for other intellectual progress, but progress can and does happen. I've developed some ideas about how to improve the system, e.g. public intellectuals could have Paths Forward and debate policies.
Is deferring to a third party, society or mainstream opinion a good system when people disagree? It's not great for figuring out what's true, but it's pretty good for keeping society peaceful: preventing violence and rights violations. If a disagreement is purely intellectual, people can just agree to disagree, have a debate, call each other idiots, or leave each other alone. The hard problems are when there is a potential for serious fighting and rights violations, in which case it's hard to come up with anything better than having people outside of the dispute decide on the outcome (and, for high stakes issues, to decide primarily in accordance with laws that were written down in advance). Many disputes deescalate because the participants already have a lot of mainstream opinions or know what the mainstream opinions are, and actual third party juries or judges can be used when necessary.
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