You Cannot See Beyond Your Valley

Muad'Dib could indeed see the Future, but you must understand the limits of this power. Think of sight. You have eyes, yet cannot see without light. If you are on the floor of a valley, you cannot see beyond your valley. Just so, Muad'Dib could not always choose to look across the mysterious terrain. He tells us that a single obscure decision of prophecy, perhaps the choice of one word over another, could change the entire aspect of the future. He tells us "The vision of time is broad, but when you pass through it, time becomes a narrow door."