AI was supposed to democratize capability — to close the gap between your strongest people and everyone else. In a lot of companies it's done the opposite: it's taken your single best employee and made them dramatically harder to replace. The person who's mastered the prompts, the workflows, and the judgment about when to trust the model is now carrying more of your operating capability in their head than any individual did before AI — and almost none of it is documented, owned by you, or visible until they're gone. Here's why your best performer became your biggest single point of failure, and what to do about it before the resignation, not after.