Communication is the key in any kind of relationship, If you don't communicate properly it may turn out to be a disaster. If you have expertise in various fields. however, if you don't know how to pitch for your expertise then no one will recognize the same and ultimately it will be a failure as you are not able to sell yourself effectively.
It can also happen when you intended to say something and by any chance, you said something else. It's more like a slip of the tongue. however, it can become a very embarrassing situation which can result in spoiling your relations. Imagine when you intend to say "How are you" but instead you say "Who are you". "How" and "Who" is a very similar words when you write them, just a shuffling letter can change the entire meaning of your sentence and a polite statement can become a very rude statement.
Similar to the above example, there are multiple instances where we wanted to say something but we end up saying something else, which can be perceived very wrongly if not said in a proper way.
I always wonder how such a thing can happen, but over a period of time I realized that it can happen if we don't correct intent to do something, let's take an example where you don't like someone, and all of sudden you meet this guy and you greet him by saying who are you instead of saying how are you.
This is quite obvious because your subconscious mind constantly trying to avoid this situation where you meet that person, however, forcefully you are meeting this guy out of force. In such case you end up speaking what you really wanted to say instead of hiding your true emotion, you say something which you should not be saying it.
Our mind is a very complex system that god has created and it's equally beautiful as well. The only issue is that we don't effectively use our minds in order to get the best outcome. The rationale of saying something is purely determined by the way we perceive information around us and the way we have experienced our life so far.
Also, It's a matter of various other things such as the person is very annoying and everyone hates him, you are talking to that person out of no choice and you have to deal with him.
The question that comes here is, in our life, we quite often land up in a situation where we are put up in such a situation that we can't avoid and have to deal with those situations.
It teaches you a good lesson to learn, effective communication is that communication which can help you to avoid certain situations, similar to this example where everyone is just trying to avoid communication with that guy, however, if you have the right skills and you know how to deal with such people by talking to them in a different way, that can help you to win over others.
Also, People are not difficult to deal with they become like that because they had their own tough time, which taught them a lesson and they started behaving differently, imagine when you are born, in fact, all of us were born similar, we never had an issue but as we grew older, the situation differed and we all started behaving differently based on hardship we have faced in our life.
The purpose of communication is to effectively present your thought but sometimes it can become a cause of disruption. All of us behave differently and the way we talk to other that becomes a general perspective of ourselves which people think about us.