When we speak, so we use the right words and tone of voice?
It is important when we speak to others, and children especially, to use the voice inflections as well as the appropriate words to convey humor, displeasure, anger or encouragement.
But when we write out those words, it even more important to use the correct ones. If we wish to be sarcastic or humorous it can be very difficult to get the emotion to reach the reader in the manner we wish. That is probably why the use of emoticons is so popular.
When speaking, my facial expression can usually display what I want the hearer to find in my words. But when writing, it can be very difficult to get the point across to the reader. But this is the job of anyone who rites.
If we tell a child to 'don't get smart' are we really telling them to be stupid? If we want to communicate with a child, it is easy to close them off with a sharp word, and they shut down. We really want them to be open to us, even if not at that precise moment.
Adults are not really much different. They both want us to listen to what they are saying. They want to be heard, and they want their words to be understood. So it is important to be a listener as well as a speaker. Tone of voice is very important here.