How was the king defeated?

Oh, that's an easy one. He grew to believe he was invulnerable.

But he wasn't? Even though nobody ever captured his castle?

That's right. As soon as he stepped out of the impregnable building—

Uh oh. But why was he so silly?

Bedtime now, sweetie. I'll tell you how I #convinced him some other day.

#MastoPrompt #MicroFiction