Customers don't know what they want. There's plenty of good psychology research that shows that people are not able to accurately predict how they would behave in the future. So asking them, 'Would you buy my product if it had these three features?' or 'How would you react if we changed our product this way?' is a waste of time. They don't know.
Eric RiesAs an entrepreneur, I knew that if my company failed, I could always try again. So I often felt that the only real risk of true financial ruin came from the possibility of a serious illness that either exceeded my insurance plans lifetime limits, or was not covered due to rescission.
Eric Ries