The art of discovering bugs in software is in identifying the misunderstandings that could be theoretically present, such as:
Between "business" and "the development team"
Between a "developer" and a "tester"
Between the organisation and its users
Between the desired effects and what was actually implemented
Between a developer and their operating environment (such as the web browser, the language runtime, etc)
Additionally, "shifting testing left" is about trying to identify these misunderstandings, and clarify them, as early as possible. The later in the process they're discovered, the more expensive it is to fix them. Many "bugs" can be fixed purely through conversations at the right moment in time - The quality of conversations drives the quality of the product
In fact, this itself is a testing process, as Testing is clarifying misunderstandings
Testing is clarifying misunderstandings
As Testing is clarifying misunderstandings we can learn quicker.
Testing is clarifying misunderstandings, not that we've built to specification
Testing is clarifying misunderstandings and through structured conversations like Example Mapping for discovering unknown unknowns can help tease out the common language.