What is a short tale that teaches a lesson?

Once, a hungry fox spotted a bunch of juicy grapes hanging high on a vine. After several failed attempts to reach them, he finally gave up and declared, "Those grapes are probably sour anyway!" This fable teaches us that people often dismiss what they can't have, rationalizing their failures to protect their pride. It reminds us to confront our desires honestly rather than belittle them when they seem unattainable.