If you want the truth of it, a “polite fiction” is a lie–or at least an untruth, a deception, a prevarication…there are many names for it. Mostly it’s a way to preserve the peace and allow things to go on as-is, without upsetting the proverbial apple cart.
Example: “We’re just one big happy family!” [Actually we’re not, but by telling that ‘polite fiction–and not mentioning crazy Uncle Binky who lives in the basement, or Miss Mew, the cousin who became a crazy old cat lady before she was even 40–most of the family can enjoy Thanksgiving dinner together and send chirpy little Christmas letters to each other.]
If you’re Southern by birth, you come into the world with a Polite Fiction gene bred into the bone and the ability to automatically upgrade to the next level as needed. The system can fail–especially with age–leaving you bereft of tact and unwelcome at social gatherings, but that gives the rest of your people (i.e. family) the chance to politely fictionalize, marginalize, and otherwise overlook your problem.
In the South, we’re never telling made-up stories…we’re telling carefully edited versions of the madness we call family, life, and business-as-usual. And we’re real polite about those fictions.