User experience theory applies to just about everything in our daily life, even something as simple as a Brita water pitcher [Image below]. If the product (or interface) is not working as expected, the user experience will be less than optimal.
When I first used this particular Brita pitcher, I discovered that it has a major design flaw. There is this section where the hollow handle connects to the reservoir, thereby permitting unfiltered water to flow down and mix with the freshly filtered water, obviously defeating the point of filtering your water! (See image below.)
It seems to me that some basic user testing would have revealed this very obvious design flaw.
This is just a small example of how easy it is to make users of any product unhappy. As a User Experience designer, my goal is to give users the best experience possible. Doing so requires user testing throughout the product development cycle in order to identify both the big and small issues so that they can be corrected before going live. I seriously wonder if this is something Brita did before rolling out this product.