A factor can stay academically valid and still become tactically painful when it gets crowded. Mechanism: Crowding does not mean the idea is false. It means the path from signal to payoff becomes more fragile because too many balance sheets are leaning the same way at the same time. Why it matters: That is usually when a clean cross-sectional edge starts behaving like a liquidity regime trade. $$ Crowd\ Risk \approx Position\ Similarity \times Liquidity\ Fragility $$ Plain English: The more similar the positions and the thinner the exit door, the more violent the unwind. Market translation: You can see it when the same "quality" names absorb too much capital and a simple de-risking wave hits them all at once. Failure mode: People often confuse crowding with valuation. They overlap, but one is ownership structure and the other is price relative to fundamentals. Review question: Write down the state variable you would monitor first if this thesis started to drift. That is usually where the edge is: not in the vocabulary, but in the structure underneath it.