What does it mean that schema debt from deferred updates?

Knowing a schema is wrong but not updating it creates a growing liability.

Example: Your mental model of your team's codebase was accurate two years ago. Since then, three services were rewritten, the data layer moved to a new provider, and the auth system was replaced. You still make architectural suggestions based on the old map. Each suggestion wastes 30 minutes of meeting time while someone explains why that won't work anymore. Two years of deferred schema updates have turned you into a drag on the team you're trying to lead.

Try this: Pick one domain where you make regular decisions: your career, your health, a technical system you manage. Write down the mental model you currently operate from. Now mark every element that hasn't been verified in the last six months. Count the unverified elements. That count is a rough measure of your schema debt in that domain.