To expand on this: the essence of politeness is to not consciously convey unpleasant thoughts, either by dodging communication on certain topics or by making use of subtext to convey them subconsciously (so as to avoid painful mutual knowledge).

A person X can, for example, turn an acquaintance Y down for a date by giving a proximal explicit reason, but do so in a subtly dismissive way that Y will subconsciously pick up on (and not ask X out again), and yet subtly enough so as not to constitute mutual knowledge of romantic rejection; Y may never consciously realize they've been rejected.

(Things get awkward when one party or the other botches such an exchange.)