When you write your presentation, you’re using your brain in a specific way, to convey messages in writing. But when you deliver that presentation out loud, you need to use the same information in a different way, to communicate with people verbally.
Unless you’re very practiced at writing the way you speak, this shift from your writer-brain to your speaker-brain can be bumpy. This is why we recommend that you always practice out loud.
When you replicate, as closely as possible, the circumstances in which you’ll be presenting, you can catch all kinds of problems before they occur. The phrase that seemed so beautiful when you wrote it turns out to be hard to say out loud. You don’t have a transition from Point A to Point B. You learn that you didn’t actually come up with an ending for your presentation, which forces you to come up with a way to close.
Take the time to say the words of your presentation out loud. It’s a gift for you and for your audience.