Consider other approaches to the problem at hand. Is the form factor that you had in mind really the best way of accomplishing the task? Is any form factor the best way of accomplishing the task? Maybe a service fits the mold better. Perhaps the answer lies within an existing product.
Example: When Sandisk wanted to provide it's customers with an affordable, compact and convenient way to transfer data from their SD cards to their computers, the best solution turned out not to be a card reader at all. LUNAR designed the SandiskUltra II Plus SD card to transform itself to fit directly into the USB slot on a computer. No cables, readers or adapters necessary. Because the problem was data transfer, not lack of card readers. Watch Out: Be sure to always consider a client's economic performance goals when applying this method. Even though a behavioral change could solve the problem at hand (like taking more pictures with your phone so they can be transferred wirelessly in this example) the client would be left with no product. Suggesting the modification of an existing product, or a service instead, may still meet their financial objectives.
Discussion: This is one of the more abstract tips in the DFGS, and can often be overlooked or pushed aside because it's hard to wrap one's mind around. The basic idea behind questioning the premise of the design is to make sure to always keep an open mind when approaching a design problem. Challenging the initial constraints (marketing, usage models, price point, basic form and function) that are imposed on a design can lead to new ideas that might very well prove to be more sustainable ideas. Nike has challenged how shoes are constructed, Heineken has expanded the conventional usages of a glass bottle, and a while ago Apple challenged the very medium of music. So why shouldn't you redefine something from the ground level up?