Real knowledge means knowing why the alternatives were rejected

Charlie Munger draws the line at Max Planck's chauffeur. The chauffeur had heard Planck's quantum mechanics lecture so many times he could deliver it himself — and did. He held up fine until a physics professor in the audience asked a follow-up question. Only Planck, with the background knowledge to support the ideas, could answer it.

You understand an idea not when you've memorized it, but when you know why its specific form was chosen over all the alternatives. Only once you've traveled the roads that were earnestly explored but ultimately rejected can you grasp it firmly and see it clearly, with all the context that supports it.

The more pressure people feel to have instant opinions on every topic, the more chauffeur knowledge dominates. In that state of intellectual insecurity, they rush to judgment and abandon the philosophical mode — becoming slaves to fashionable ideas and blind to their own unconscious assumptions.

Type	What you can do	What stumps you
Real knowledge	Answer follow-ups, handle edge cases, explain why alternatives fail	Nothing inside the domain
Chauffeur knowledge	Recite the talk fluently	Any question outside the rehearsed script

Source claim: You have real knowledge of an idea only when you know why its specific form was chosen over the alternatives — not just when you can recite it.