Two important needs humans have are certainty and variety. Though certainty matters because people need to trust you to take them somewhere, variety matters a great deal because people get bored if they can predict what’s next. At every level of your writing and communication, you need to offer variety. You do so by changing the variables you are using. Variables can be themes, paragraph length, sentence types, and much more. Once you understand the variables of writing and communication, you can vary them and make your writing engaging.