What does it mean that a schema is a mental model made explicit?

A schema is a mental model that has been externalized, named, and structured so it can be examined, tested, and improved — turning invisible cognitive habit into visible cognitive infrastructure.

Example: A product manager navigates every prioritization meeting using an implicit mental model: 'urgent customer complaints always outweigh long-term roadmap items.' She has never written this down. She does not call it a rule. But it governs every decision she makes. The moment she writes it on a whiteboard — 'My prioritization schema: reactive customer pain > proactive roadmap investment' — it becomes an object she can inspect. Is this always true? Under what conditions should the roadmap win? What evidence supports this weighting? The mental model existed before. The schema exists now — explicit, testable, improvable.

Try this: Identify one recurring decision you make at work or in life — how you choose what to work on first, how you evaluate whether a meeting was productive, how you decide what to read. Write down the rule you actually follow (not the rule you think you should follow). Name it: 'My [domain] schema.' Look at what you wrote. Is this the schema you would design on purpose? If not, what would you change? You have just made a mental model explicit. That is schema construction.