This isn’t to say that a person can’t, to some extent, develop within themself that instrument of assessment (which is part of the mental apparatus of each of us), but that not everyone is equipped with the same aptitude, or reach, with regard to what that instrument does. Or, anyway, not everyone’s instrument is in a condition of health, or is ‘sound,’ as the philosopher David Hume might have said. (He wrote about this centuries ago, in his essay Of the Standard of Taste).