It is a Speak Simple founding principal developed through trial and error, “Talk to your Grandpa”.
Speaking to the elderly is sometimes more difficult than anything else. For those senior citizens like my own grandfather who has not adapted to digital cameras, it is extremely difficult to explain how all those pictures got on this thumbnail size piece of plastic, or how I can find the number for the pizza restaurant using my phone. Sometimes the audience is just like my grandpa, they need a bit more tender loving care when it comes to explaining things and then elaborating on them. Even more difficult when grandpa forgot about it when you told him yesterday.
It’s an ideal situation to speak not only slowly but in simplified terms just like you would if you were talking to your own grandparents. If you are speaking to any group outside of your colleagues, you should assume they have only a little information about the topic and plan to teach them yourself, then build on the information. As a speaker, you should be talking the audience or else you are speaking to yourself. If your audience doesn’t understand what you are talking about from the get go, then you’ve lost them and as the complexity of the information increases they won’t be paying attention. Those lost souls are going to be focused somewhere else, probably on smart phones, these days it’s easy to be distracted. When preparing for your next presentation, would your grandpa understand?