Trade consists of correcting errors. That's why it's profitable.
The errors are errors about who has what property.
As with all error correction, criticism and knowledge are central.
All trade requires knowledge: you have to know that it'd be a good idea to trade X for Y or you won't do it.
All trades require criticizing and wanting to change the status quo. I haven't got an iPad, *but that's a mistake*, I should have one! I haven't got anything to eat for dinner, but I should change that! Or more advanced, "That company is doing some useful stuff, but I have an even more valuable project for them to work on than their current one, so I'll buy them out and change their focus" or "That store is doing ok but if i owned that particular building I could provide more value there, so I'll buy it".
When you're right, you buy a store (say) for $110, that had a value of $100 to the old owner, and then you make a profit of $200 from it. So by correcting the error (store being used in a way with $100 of value instead of the new way worth $200), value is creating and both parties to the trade gain.
When you're mistaken -- i.e. you don't correct an error -- then you buy for $110, but only make $90. So you come out behind. But at least your mistake didn't hurt the other guy, it's only your problem, which is good.
In this way, correcting errors is encouraged, and creating errors is discouraged.
A mistake made by Ayn Rand and some libertarians is to think it's simple to decide what is and isn't force.
Consider these example situations:
1) A biker is forced to steer well around a car being washed or else be hit with some water.
2) A car door is opened 10 ft in front of a biker who steers around it. The biker didn't see the driver look first.
3) Some amateur bikers go slowly blocking the road. They choose not to go single file to let people pass.
4) A car doesn't use a blinker when it should.
5) A baseball field is built so that home runs which clear the fence could hit people at a nearby park.
In each case, it is not obvious if force is being initiated. That means the principle "don't initiate force" isn't a panacea, because reasonable people can disagree about what force is.
One of the crucial mechanisms of a peaceful, civilized society is that people in general make a reasonable effort to avoid doing anything in the grey zone which might be taken as force, but at the same time if someone does do something borderline bad they do their best to overlook it and not get upset. Almost everyone having a double standard in this way (aim for one standard, but accept things up to a worse standard from others) is really effective. People don't suceed at this every time, but it's a major source of confliction prevention.
Another mechanism of our society is to treat the same action differently depending on the person's intention. Was it an accident or intended? Was he trying to accomplish a legitimate purpose that people should accomplish, or not? If you hit someone while playing baseball that's one thing; if you just find a fence with people on the other side and start hitting balls over that's another.
It's important to be tolerant of impositions others impose on us, and to expect them, not to just draw a line and become hateful and aggrieved if anyone crosses it.
One underlying reason this attitude is effective is that conflict resolution and negotiation is expensive. I don't have in mind only courts, but even simply talking to a stranger, and making them understand the issue, can be hard. They don't know what's on your mind, or what kind of things you care about or expect from life, and they may well assume if you're talking to them it must be important and so misunderstand any small complaint.
1688, liberty was (re)invented. In England, having been brewing there for many centuries, with many setbacks.. (It had previously existed in ancient Greece, especially Athens.)
A hundred years later, Anglophiles in France wanted it too. They advocated liberty and explained why it was a good idea to the French.
Many Frenchmen were confused, impatient, angry, and ignorant. The French philosophers did not understand liberty as well as the English did, and the French peasants understood much less than that.
As the revolution began, most of England thought the French were finally catching up and becoming more like England. That's what the better French philosophers hoped for.
Unfortunately, the mainstream French approach had several crucial mistakes. Edmund Burke noticed these mistakes and wrote a book explaining them and also making accurate predictions about the violence that was to come. As William Godwin put it, "Mr Burke is entitled to great applause for having seen earlier than perhaps any other man the events the seeds of which were sown in the French revolution."
Burke was a lifelong advocate of reform in England. He would have liked France to have liberty too. But as Burke understood, there are different approaches to reform, some of which are effective, and some of which are ineffective or worse. Wanting liberty is not enough to get liberty; misguided approaches typically lead to disaster.
Burke carefully explained in his book that the French approach was not following the English lead, but instead was doing many things quite differently. Of particular note, the English way was to attempt gradual reforms; there should be no sweeping changes unless that is the only possible way forward. France had already been reforming; the King had implemented some reforms and was somehwat sympathetic to liberty, as were many of the aristocracy; so why, then, was there any revolution at all? The French Revolutionaries threw away progress in hand for unrealistic dreams of shortcuts to much larger progress.
Burke also explained that the French made mistakes in political philosophy. They didn't understand how important it was to build on existing traditions, and improve on existing political institions. They thought they could build new things that would be better, but that is folly for any new thing is bound to have its own problems; the way we get good things is not about sweeping away all existing institutions and doing it right once and for all, but about correcting errors.
Burke respected the value of the men and ideas that came before him, and hoped to do even better. Many of the French did not respect their existing ideas, and didn't see any value in them. Because they failed to understand the valuable parts of their existing system, they failed to incorporate those useful parts into their new system.
The French wanted fast progress, but shortcuts don't work. As Godwin explained, if you change a country overnight, but the populace does not understand the new way, they will simply follow their existing ideas and revert things back to the old ways. Reforms must come after knowledge; they must be understood first and implemented second. In this way, reforms happen easily, almost automatically, after most people already want them, instead of being a struggle, and there is no problem of reverting. This way has a further large advantage: if we have a new idea and implement it right away, it might be a mistake. If we first persuade most people in the country of the idea, then in all that discussion we may improve the idea or reject it; error correction happens in the persuasion phase.
Due to its mistakes, the French Revolution became a violent mess that set liberty back not only in France but also in the rest of Europe, and even in England where it disheartened many reformers and, due to a real danger of revolutionary violence, temporary suppression of open debate was deemed necessary.