When you truly understand what job people are really trying to get done by using your product, then you can focus your efforts on meeting that need. Asking customers what job they really want done can tell you the root of their problem and eliminate faulty assumptions on either side, ultimately resulting in a solution with a higher chance of success. In your analysis, you want to figure out what job your product is really currently doing and where it might be miscast, as in the milkshake example (see 5 Whys in Chapter 1 for a tactical technique).
