The Left Hand of Darkness (1969)

A diplomat who cannot read the culture he is sent to persuade is the whole tension of Le Guin's 1969 novel. Genly Ai is the lone envoy of the Ekumen, a league of worlds, sent to invite Gethen to join it: an ice-age planet whose people have no fixed sex and are neither male nor female for most of each month. The king's court in Karhide and the bureaucrats of Orgoreyn each treat him as a lever, and he misjudges both, because both run on shifgrethor, an unspoken code of prestige and face under which even an ally will not tell him plainly that he is one. A long stretch on the ice later in the book trades the courts for something more personal. It won both the Hugo and the Nebula.