We want our users to achieve their goals with minimal friction. Usability is defined as the quality of a product's ease of use. Usability depends on how your product design aligns with the different user needs: the needs from our human condition, the needs from general expectations, and those from the specific context of use. There are usability guidelines that capture general principles, but they cannot include all the context-specific considerations that make your product unique.
In order to check whether your ideas work in a specific context, you need to test them in such context. Usability testing is a process used to identify the most relevant issues in the usability of a product. Usability testing is not aimed at discovering all issues, or to provide you with accurate statistics on how many users are affected by a given issue...