In engineering, an invariant is a condition that must remain true for a system to function correctly. Violate the invariant, and the system fails, regardless of how elegant its other features might be. A bridge can be aesthetically beautiful, use the finest materials, and employ the most innovative design principles, but if it violates certain structural invariants, it will collapse. The invariants don’t negotiate. They don’t care about your intentions. Instruction has invariants too. There are non-negotiable conditions for learning to occur reliably, conditions that emerge not from pedagogical fashion but from the architecture of human cognition itself. Most educational apps violate these invariants routinely, systematically, and, one suspects, knowingly. They do so because compliance with these invariants conflicts with the metrics that drive their business models: session time, completion rates, user satisfaction, and the holy grail of engagement.