Disagreements are fundamentally human. Misunderstandings even more so. They often lead to frustration, and sometimes wars. The root cause isn't always clear to both parties. Sometimes the parties disagree, sometimes they misunderstand each other, and sometimes they confuse the two.
Disagreements arise from divergent view points. By way of illustration, let's say that Roger and Karen work for a company that wants to build flying cars. Roger likes the idea of flying cars but Karen would rather cars not fly. Karen has her reasons for not wanting the company to make flying cars, reasons which she may or may not state. But reasons aside, she just doesn't think cars should be allowed to fly. Roger may think that Karen simply doesn't understand why flying cars are such a great idea. The problem here is that understanding and agreeing are two different things. For example, Roger believes that flying cars will earn the company a lot of money. Karen understands the potential for financial gain, but she believes that safety concerns supersede monetary gain. One may understand a viewpoint, but still disagree with it.
Misunderstandings tend to be even more complicated. Let's introduce Alicia. Unlike Karen, Alicia likes the idea of flying cars. But as an engineer, Alicia knows that there are limitations which prevent the company from making flying cars. She may present these reasons, and explain that while flying cars are a great idea, the company can't build them just now. Roger of course disagrees. He thinks that the engineers can do anything they set their minds to, and that they should just get it done. This situation may quickly deteriorate as both parties get annoyed with each other. This is a disunderstanding.
Disunderstandings arise when one party misunderstands the reason for a disagreement. In this case, Roger and Alicia disagree on the issue of whether the company should make flying cars. But Roger misunderstands Alicia's reasons for not wanting to pursue the project. In his mind, there is no distinction between Alicia and Karen. He confuses real limitations, which he may not understand, with an unwillingness on the part of the engineers.
To avoid disunderstandings, both parties should seek to understand the other's position. Only then will they be able to differentiate between a disagreement based on personal preference, and one that arises from constraints. Despite best efforts, sometimes one party just won't get it. In this scenario, a conciliatory approach may be best. Or just ignore them until they get some sense, or go away.