cautionary

A cautionary tale or warning is one that teaches us about a potential problem or danger so we can avoid it.

When people talk about something being "cautionary," they usually mean that it's meant to warn others about possible risks or consequences. For example, a movie with a strong message might be described as a cautionary story because it shows what happens when someone gets into trouble due to their own actions. A politician might give a speech that's more like a warning than an encouraging pep talk – this is likely a cautionary address. In either case, the idea is that the person giving the message wants others to think carefully and make good decisions based on what they've learned from the story or experience.