Every mental model you use fluently has a hidden cost: it forecloses the questions you no longer think to ask. The German physiologist Johannes Müller documented this in 1838 through what he called the 'specific energies of nerves' — the discovery that the nervous system doesn't transmit reality directly; it transmits only the particular signal each nerve is built to carry. Stimulate the optic nerve mechanically and you see light, not pressure. The nerve doesn't lie — it just speaks its one language regardless of what touched it. Product managers face the same constraint. The model you've trained yourself to reach for — jobs-to-be-done, systems thinking, whatever framework shaped your early wins — doesn't distort your perception maliciously. It faithfully reports back in its native signal type. The trap isn't the model being wrong; it's the model being fluent. Fluency is what stops you from noticing the signal it cannot carry. The practical move isn't finding a better model — it's periodically asking: what type of input would this model be structurally incapable of registering, even if it arrived clearly?

What is the last piece of product evidence you received that felt irrelevant or noise — and which model were you holding when you made that call?

Drawing from German Sensory Physiology / Philosophy of Perception — Johannes Müller (Handbuch der Physiologie des Menschen, 1833–1840)