I Added a Paragraph to My AI Character's System Prompt. She Invented a Different One.

I spent years in the gaming industry learning that characters are the reason people come back. Features rot. Graphics age. A character people can't stop thinking about outlasts every mechanic. Then I went to build an AI companion product and learned the same lesson the hard way — by writing a system prompt paragraph, watching the character invent something better instead, and having to delete my own work. Here's the experiment, what actually happened, and the prompt-engineering rule I now run ev