What makes the exposure acceptable? What makes the exposure pleasing?
While the standards of one photograher are often at least a bit different from the standards of another, it's often the case that a group of people share many of the same standards in common.
This can be illustrated by a shared respect for traffic laws. I'm not talking about strict adherence to those laws but the common practice in many communities of drivers being observant enough that avoidable accidents are kept to a minimum.
In the same vein, the photographic community may not universally agree on a precise list of standards that determine a "proper exposure," but people share enough in common that a productive discussion of those qualities can be had.