familiarity

A man should avoid displaying deep familiarity with any subject. Can one imagine a well-bred man talking with the airs of a know-it-all, even about a matter with which he is in fact familiar? ... It is impressive when a man is always slow to speak, even on subjects he knows thoroughly, and does not speak at all unless questioned.

KenkĊ "Essays in Idleness" (79) As translated by Donald Keene