Do you know the difference between a want and a need? It can be a hard thing to understand, especially when you want something so much that you feel like you have to have it. But some things aren't essential--like jellybean tacos and groovy boots. Other things are essential--like fuel and feet to put the boots on. The robots in this book are here to show you the difference as they make trades to get some things they really want (hooray!) but give away some things they need (oops!).