Product development has traditionally had an “if you build it, they will come” attitude. Usability has often followed suit, producing products and user interfaces that worked beautifully when tested in a lab. Unfortunately for designers, product developers, engineers, etc., people do not use products in a lab. No do they use them as we might intend. They use them in the real world, which is filled with distractions and stresses that can have a tremendous impact on use, usability and basic comprehension. If you don’t account for these external influences when designing and testing, you run the risk of building products that fail in practical settings, no matter how well they performed in the lab.
Good design stems from a holistic understanding. The benefit of ethnography’s holism is a multi-dimensional understanding of users, consumers, shoppers, or whatever label we impose. The key point (and the most difficult one for most of us) is to avoid observations that reflect only our own cultural experiences and ways of thinking about how humans come to solve problems and interact with the world. It’s about constantly remembering to explore a problem from different angles. You have to make sure an observation is consistent within a pattern of contextually grounded observations, not just a dramatic anecdote or something that confirms your view of the world.