When your mental model of a situation stops working, the instinct is to patch it — add a new rule, refine the edge case, update the heuristic. But the 14th-century logician Jean Buridan noticed something uncomfortable: a model that has been patched enough times doesn't fail dramatically. It just quietly stops generating genuine predictions and starts generating post-hoc justifications. You're no longer using the model to think; you're using it as a defense attorney. Buridan's work on 'suppositio' — the way terms carry different referential weight depending on context — pointed to how the same conceptual structure can mean completely different things in different situations without anyone noticing the switch. The practical hit here: the sign that a mental model has crossed from tool to rationalization isn't that it gives wrong answers. It's that it stops giving falsifiable ones. If your model of your team, your users, or your market can explain any outcome after the fact, it isn't a model anymore — it's a mood. Try holding your current working model up to this: what would have to happen next week to prove it wrong? If nothing comes to mind, you're not thinking with it. You're hiding behind it.

Name the mental model you've invoked most often in the last month — then write down one specific event from that period it cannot explain.

Drawing from Late Medieval Scholastic Logic / Nominalism — Jean Buridan (Summulae de Dialectica, c. 1330s)