Why it is important to observe an individuals reactions when communicating with them?

When you are observing an individuals reactions while communicating it's important to pay attention to their facial and bodily reactions because only about 70-80% of communication is verbal, meaning that you are going to miss out on a large part of communication if you are not paying attention to peoples facial and bodily reactions.

In communicating you are not talking to yourself, of course you are talking to someone else. So maintain the atmosphere and his/her feelings by observing reactions. You don't want to be annoyed don't you, same goes to them. :)