There is a difference between what you think and what your users think. The belief held by your users about how a system works is called “Mental Models”. A classic example of this is the CD-ROM in the main frame of the classic tower computers. The purpose of the CD-ROM drive is to hold CD, obviously, but there are lots of cases where users even use it to hold their drink cups, which often spills the drink and damage the computer. It is common that the system your team designed may be different in the users’ hands as they might hold different opinions of how it should work. That’s why user tests are so crucial in the field of design. This is an essential way for us to dive into the mind of users and test the usability of the system in real-life scenarios.