The 'What Customers Need' Fallacy

Here is a simple puzzle for you: If you start with 'What customers need' - you will only build incremental stuff, because what the customer needs is always based on what they have right now. To build revolutionary products, starting with what customers need is a very bad starting point. Steve Jobs was right when he said that the customer does not know what he needs until you build it and show it to him, for the simple reason that he does not know what is 'possible'.

But then if you start building stuff without knowing if the customer needs it, how do you know they will need it when you have built it?

So the puzzle is this: where do you start?