Wiktionary
n. A story told in folklore to warn its hearer of a certain danger.
Wikipedia
A cautionary tale is a tale told in folklore, to warn its hearer of a danger. There are three essential parts to a cautionary tale, though they can be introduced in a large variety of ways. First, a taboo or prohibition is stated: some act, location, or thing is said to be dangerous. Then, the narrative itself is told: someone disregarded the warning and performed the forbidden act. Finally, the violator comes to an unpleasant fate, which is frequently related in expansive and grisly detail.
Usage examples of "cautionary tale".
Maskelyne is the pure type of one who would transcend the Earth, making him, for Mason, a walking cautionary Tale.
I bid you good folk to hear this cautionary tale, and leave this place the wiser for it.
It was a cautionary tale that had been handed down through the ages.
Terpstra capable of running a shadow project, but with Dempsey's cautionary tale about her, anything was possible.
It's a cautionary tale, warning of the evils of rampant heterosexuality.
This is also a cautionary tale, intended to say You are not alone.
I wasn't telling myself a cautionary tale or gloating over my survival.