The desktop metaphor — files, folders, the trash can — is the most successful mental model ever deployed in consumer software. It worked because it mapped an unfamiliar digital system (file storage) onto a deeply familiar physical one (the office desk). Users did not need to learn an abstract taxonomy; they already knew how desks and filing cabinets worked. The interface inherited the mental model rather than building a new one from scratch.
When a design violates a user's mental model, the result is confusion or error. The confusion is often described as a "bug" or "poor UX" when the actual problem is a mismatch between the system's actual model and the user's expected model. Disclosing the gap between these — making the actual model legible and predictable — is one of the core tasks of interaction design.
Mental models are not universal. Expert users and novice users hold different mental models of the same system. Power users develop richer, more accurate models over time, and their UX needs evolve accordingly: what helps a novice (explanatory text, confirmations, guided flows) can frustrate an expert (unnecessary friction, reduced control). Designing for multiple mental model levels simultaneously is one of the enduring challenges of product design.