The first four reasons are about the investment; reason 5 is the only one about you and your portfolio. A successful position compounds, and as it does, its weight in the portfolio grows. An 8% position that five-bags becomes, all else equal, roughly a third of the portfolio. Now a single company's idiosyncratic risk (a fraud you cannot foresee, a regulatory shock, a technological disruption) threatens the whole portfolio, not just a slice (M9.01: risk is probability × magnitude of impairment; a 30% position turns a company-specific 50% drawdown into a 15% portfolio hit). The business can be wonderful and fairly priced and you still act, because concentration risk is real and lives in your portfolio regardless of the merits of the stock. This is the reason that has nothing to do with the company and everything to do with the sizing discipline of M9.01 and the concentration policy of M9.02.
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What is the decision test for a trim?
The decision test: does the position exceed the maximum single-position weight I set in advance in my concentration policy? If yes, the action is almost always trim, not exit: reduce the position back to your cap, and no further. This is the crucial distinction that separates reason 5 from the other four: reasons 1, 2, and often 3 say "the reason to own this is gone → sell it all"; reason 5 says "the reason to own this is fully intact, I simply own too much of it → sell the excess and keep the rest working." Trimming a winner back to your cap is being a Connoisseur and a risk manager at once: you keep the compounder compounding while capping the impairment it can inflict. Exiting a great, intact position entirely because it "got big" is the Raider's error dressed as prudence. You had a winner and you killed it.
How do you set the cap and trim efficiently?
Three refinements: (a) the cap is a policy set in the cold state, not a number you invent under the influence of a big gain. This is why M9.02 makes you write your concentration policy down (e.g., "no position above 20% of the portfolio at cost-of-trim, or above 25% by drift, for a high-conviction idea"; tighter for lower conviction). (b) Mind the tax and trim efficiently: sell the highest-cost-basis lots first where jurisdiction allows (US specific-lot identification), use the long-term-rate portion, and consider trimming gradually across tax years so the risk reduction and the tax bill are both managed. Never let the tax tail stop a genuinely necessary risk reduction. (c) Reason 5 and the compounder caveat (see selling above value and selling compounders too early) are in productive tension: reason 5 says trim the oversized winner; the Connoisseur says run winners. The resolution is that reason 5 asks you to trim only the excess over your cap, not to sell the position. You remain fully exposed up to your maximum tolerated weight and only shave what pushes you past the risk you decided, in advance, you could live with.
Worked example: trimming back to a 20% cap
Worked example (illustrative). Your portfolio is ₹1.32 crore. Years ago you bought A at an 8% weight; it has five-bagged and is now worth ₹40 lakh, while the rest of the portfolio was roughly flat, so A is now 30.3% of the portfolio (40 ÷ 132). Your written concentration cap is 20%. Target A weight in rupees = 20% × ₹1.32 crore = ₹26.4 lakh. Trim = ₹40 lakh − ₹26.4 lakh = ₹13.6 lakh sold, ₹26.4 lakh kept (still 20%, still compounding). Because A cost you ₹8 lakh and is worth ₹40 lakh, 80% of any sale is gain: the taxable gain on the ₹13.6 lakh trim is ₹10.88 lakh, and LTCG at 12.5% is ≈ ₹1.36 lakh in tax (before the ₹1.25 lakh annual exemption). You have capped single-name risk at your policy weight, kept the bulk of the compounder working, and paid a modest, deliberate tax to do it. Note what you did not do: you did not exit a wonderful, intact position because it had done well. That would have been the Raider clipping the flower.