No One Buys a Quarter-Inch Drill Because They Need a Quarter-Inch Drill.

No one buys a quarter-inch drill bit because they need a quarter-inch drill bit. What they need is a quarter-inch hole. But you don’t really need that. What you need is to put the shelf on the wall. But you don’t really need that. What you need is a place to put the books that are cluttering your bedroom. But you don’t even really need that. What you need is the way you will feel when your spouse thanks you for cleaning things up. What you really need are safety and security and a feeling that you did something that was important. This is what we sell.

This example beautifully explains the process of peeling the onion, to keep our eye on the main goal. The reason people purchase a particular product or service, and what it's really for.