Duarte explains that great presentations share the same basic shape - a movement between what is and what could be. She analyzes Steve Jobs' iPhone launch keynote and MLK's I Have a Dream peech - and demonstrates how - in very different ways - both speeches share that up-down shape.
While I find her analysis fascinating, what interested me even more was her ultimate takeaway: This is the shape of overcoming obstacles. By moving back and forth from what is to what could be, the speaker enables the audience to move past the resistance of the present reality - and into the possibilities for the future.