It is partly subjective, often the inspector has to judge whether a product passes or not.
Example: An inspector who discovers a slight burn on a surface must decide whether a tight or loose fit change, even with micrometers, is bad enough to justify rejecting the measurement by 0.0006 inch. The inspector's design is important because he enforces quality standards.
Fatigue and Monotony can affect any audit decision.
Inspection only separates good and bad items. There is no way to prevent the production of bad items.