The iceberg above the water represents the content that makes it into your speech or presentation. The glacier beneath the water represents what you know about your topic that doesn't make it into your presentation. The iceberg will only stay afloat if it is held up and supported by the glacier. Same way with your presentations.
Authenticity Rule #2 is Know Your Content. Presenters who are able to present with the presence and grace of an iceberg have an entire glacier of expertise, study and knowledge holding them up.