What is your favorite movie? Is it a Steven Spielberg action flick? Is it a Nora Ephron romantic comedy? How often have we seen reviews from professional movie critics that either applauded a film or gave it a negative review, but then the commercial success of the film is quite the opposite of the reviews? We like certain films because there are things in them that speak to us. And to that end, we are all critics. We all have opinions on the films we watch. We also have opinions about the software we consume. You probably have software you like and software you hate to use, even if you can’t explain why. In this chapter, we will focus on what we can do to reduce the volatility (and subsequent rework) in the design and development of user interfaces.