When you're a carpenter making a beautiful chest of drawers, you're not going to use a piece of plywood on the back, even though it faces the wall and nobody will ever see it. You'll know it's there, so you're going to use a beautiful piece of wood in the back. For you to sleep well at night, the aesthetic, the quality, has to be carried all the way through.— Steve Jobs, explaining something his father taught him

Check out this article on Fast Company, which describes the 6 Pillars of Steve Jobs' Design Philosophy.