Interestingly, an almost identical proverb exists in Polish ("him" is replaced with "swine" canonically, but it's often replaced by a person's name). It's used to suggest that someone is either too dumb or too self-assured to accept criticism. Is the intended meaning similar in Greek?
It's hypothesising a phenomenon. I'm looking for a measure. The phenomenon is intuitively correct, but also suspiciously attractive. Sort of like the bullshit-job (or corrupt-bureaucrat) hypotheses, where every job or public official one doesn't like can be conveniently terms bullshit absent any rigour.
But if you feel like it's raining, it probably is.