We include many activities, because your brain is tuned to learn and remember more when you do things than when you read about things. And we make the exercises challenging-yet-do-able, because that's what most people prefer.
We use multiple learning styles, because you might prefer step-by-step procedures, while someone else wants to understand the big picture first, and someone else just wants to see an example. But regardless of your own learning preference, everyone benefits from seeing the same content represented in multiple ways.
We include content for both sides of your brain, because the more of your brain you engage, the more likely you are to learn and remember, and the longer you can stay focused. Since working one side of the brain often means giving the other side a chance to rest, you can be more productive at learning for a longer period of time.
We include challenges by asking questions that don't always have a straight answer, because your brain is tuned to learn and remember when it has to work at something.
Finally, we use people in our stories, examples, and pictures, because, well, you're a person. Your brain pays more attention to people than to things.