People are very opinionated creatures. If you are a UI & UX expert, or a designer/developer, it is so easy to get caught in the cycle of making ultimate decisions based solely on past knowledge and experiences. The problem is, every scenario is different so past knowledge and experience won't always give you the correct answer. All it can do is help guide you into the right direction. This is where user-testing comes into play. A construction company for example is not going to have the same "answers" as a web design firm.