The first secret of design according to Tony Fadell is to focus on the user experience. He believes that design should be centered around the user and their needs, rather than the product itself. He encourages designers to think about how the product will be used and how it can make life easier
From Wikipedia
Anthony Michael Fadell is an American engineer, designer, entrepreneur, and investor. He was senior vice president of the iPod division at Apple Inc. and founder and former CEO of Nest Labs.