A misconception that some developers hold about testing and quality assurance is that the role of the tester is to validate that the implementation matches the design and/or the documented requirements. The symptoms of this misconception is when a reported bug gets marked as Working As Designed or Meets Requirements, or rejected as an Edge Case that is unlikely to happen in production use.
One of the roles of testers is to act as a User Advocate who protects the interests of the end users. Product owners, analysts and developers sometimes forget that the main goal for software is to improve the life of the users of the software. They can become locked into their own ideas or the existing software architecture and end up creating a sub-optimal user experience.