What is the reason for barriers to communication?

What is the reason for barriers to communication?
Every individual is coming from a different point of view. Their point of view may not be shared by the person they are trying to communicate with. Even individual works may have a slightly different meaning to the two parties.

A person imparting knowledge may have a deeper background on the subject than the learner. The speaker may think certain background information is shared but the learner may not have that information.

Emotions can get in the way. One party may be afraid, hurt, or upset by something said and the other party may not be aware of this.

Some people tend to say what they think the other person wants to hear rather than the frank truth. Some people hear what they want or expect to here even though the words used point in some other direction.