One possible moral could be the importance of listening to wise advice. If the king in the story is foolish because he ignores the good counsel of his advisors, then it shows that we should be open to the wisdom of others.
In the 'the foolish king short story', there could be a moral about the value of self - awareness. If the king is foolish because he doesn't understand his own limitations, then the story might be trying to tell us that we need to be aware of what we can and can't do. Another moral could be related to the consequences of greed. If the king's foolish actions are driven by greed for more power or wealth, then it warns us about the negative impacts of excessive greed.
Perhaps it's about the danger of pride. The foolish king might be full of himself and think he can do no wrong. So a moral could be that excessive pride leads to bad decisions and downfall. Also, it could teach about responsibility. As a king, he has a duty to his people, and if he fails in that due to his foolishness, it shows that we all have responsibilities that we can't neglect.