R — Original Text (Reading)
"Every day's closing price is our opportunity cost; not selling is equivalent to buying, otherwise you could buy something else." "No matter when you sell, don't connect it to your purchase cost. There may be many reasons to sell, but the only reason you shouldn't use is 'I've already made money.'" "Theoretically speaking, holding = buying is not actually an opinion but a fact." "What you invest in is actually based on opportunity cost."
— Duan Yongping, Chapter 5 Valuation Logic · Sections 5-6
I — Methodological Skeleton (Interpretation)
- Holding = buying is a fact, not an opinion. Not selling a stock today is equivalent to buying it again at today's market price. Your money is not "trapped in there"; rather, you are actively choosing to continue holding at the current price.
- Cost is sunk. The purchase price is irrelevant to the sell decision. Whether you bought at 50 yuan or 100 yuan, there is only one benchmark for today's decision: at the current price, is this stock still your best choice.
- Opportunity cost is the unified standard for buying and selling. You sell not because you've "made enough" or are "too afraid of losses," but because you've found a better alternative. "Cheap enough or not" is determined by your own opportunity cost—where else can you obtain a higher long-term return.
- Look back from 10 years later. Filter the anxiety caused by short-term stock price fluctuations through a 10-year perspective. If this company is still strong 10 years from now, today's rise or fall doesn't matter.
- "Not selling" does not equal "never selling." If you discover you bought wrong, sell immediately; if you find a clearly better alternative, switch positions—but never make a decision because of unrealized gains or losses.
A1 — Application in the Book (Past Application)
Case 1: "Not selling is equivalent to buying"—switching from Zhongwang to Moutai
- Problem: Company colleagues bought China Zhongwang (about 3 yuan). After on-site research, Duan Yongping judged that the business model was mediocre and the corporate culture was mediocre, and advised selling and switching to Moutai or Apple.
- Use of the methodology: Most people who heard the advice switched quickly, but some were reluctant to sell, always feeling that "there will be a chance"—this is a typical sunk cost trap (unwilling to acknowledge existing losses).
- Conclusion: "In the blink of an eye so many years have passed..., the opportunity cost is huge." Zhongwang fell to 1.46 yuan, while Moutai and Apple rose enormously over the same period.
- Result: Those who did not switch not only lost principal, but also lost the enormous opportunity cost of being able to invest in good companies.
Case 2: Holding NetEase for 8-9 years for a 100x return
- Problem: NetEase rose from about 1 yuan to more than 100 yuan, and throughout the process there was the temptation to "take profit" every day.
- Use of the methodology: Duan Yongping "may be tempted by the selling price every day," but resists it with the principle that "selling a stock has nothing to do with cost." The only criterion is "the future cash flow of the company and its business"—not the purchase cost, not PE/PB. When NetEase rose to 20-30 times, he continued to add more.
- Conclusion: He sold NetEase not because he had "made enough," but because he "needed to switch to GE and Yahoo"—driven by opportunity cost, not by take-profit logic.
- Result: A 100x return.
Case 3: Reflection on Delta Air Lines—"Sold Apple to Buy an Airline"
- Problem: Duan Yongping used the extra cash to buy 1% of Delta Air Lines.
- Application of the Methodology: Reflect using the holding = buying perspective—"From the perspective of buying = holding or holding = buying, when I bought the airline at that time, it was actually equivalent to selling Apple to buy the airline." From a 10-year perspective, this was not a good decision.
- Conclusion: "It seems a little speculative impulse in my heart stirred." Holding the airline was "uncomfortable" because "I didn't know which side time was really on," whereas holding Apple, "no matter how the stock price falls, I wouldn't mind."
- Result: Followed Buffett in selling the airline, admitting the judgment of the business model was wrong.
A2 — Trigger Scenarios (Future Trigger) ★
In what situations would a user need this skill?
- Take-profit/stop-loss dilemma: The user holds a stock that has already gained (or lost) a certain percentage, and is hesitating about whether to sell, basing their thinking on the ratio of unrealized gain or loss rather than the company's value.
- Hesitation about switching positions: The user has found a possibly better target, but because the current holding "hasn't recovered yet" or "has already gained and they can't bear to sell," they keep delaying the decision.
- Holding anxiety: The user feels uneasy about existing holdings because of market volatility, frequently watches the stock price, but has never thought about it from the perspective of the company's fundamentals and opportunity cost.
Language Signals (activate when these appear in the user's words)
- "I've already made X%, should I take profit"
- "This stock is still at a loss, I can't bear to cut it"
- "Afraid it will rise if I sell, afraid it will fall if I don't" / "I don't know whether I should switch"
Distinction from Adjacent Skills
- Difference from
dcf-valuation: The DCF skill addresses "how much this company is worth," while this skill addresses "at the current price, is holding it my best choice." DCF gives a value judgment; opportunity cost makes the buy/sell decision. - Difference from
ownership-mindset: The business owner perspective addresses "what to buy" (with what mindset to view stocks), while this skill addresses "when to buy and sell" (with what criteria to make decisions). - Difference from
equanimity-mindset: The equanimity skill handles emotional management, while this skill handles decision logic. The two are often triggered at the same time, but this skill provides an executable decision framework, not emotional reassurance.
E — Executable Steps (Execution)
After the skill is activated, the agent should execute the following steps:
-
Strip out sunk costs
- Require the user to completely ignore the purchase price, holding period, and ratio of unrealized gain or loss
- Completion standard: The user can re-examine the decision from the perspective of "if I now had an equivalent amount of cash in hand"
- Suggested phrasing: "Suppose you sold your entire position today at market price and were holding cash in hand—would you buy back in at the current price?"
-
Identify and compare opportunity costs
- List the user's current holdings vs. the best available alternatives, and compare long-term return expectations from a 10-year perspective
- Completion criteria: The user can clearly state two numbers: "the expected return of holding" and "the expected return of the alternative"
- Stopping condition: If the user cannot name any alternative (holds only one stock and knows no other companies), skip to step 3, recommend continuing to hold and expanding the circle of competence
-
Use holding = buying to make the final decision
- Ask the user: "If holding = buying at the current price, would you still be willing?" If willing → hold; if not willing → sell or switch positions
- Completion criteria: The user gives a clear hold/sell/switch decision, and the reasoning is related to company value and opportunity cost, rather than unrealized gains or losses
B — Boundary ★
Do not use this skill in the following situations
- When the user is still unable to judge company value: The premise of opportunity cost comparison is being able to judge the respective long-term returns of "holding" and "the alternative." If the user knows nothing about the company, the opportunity cost framework cannot be put into practice — one should first return to
good-businessorcapability-circleskill。 - Purely short-term trading decisions: This framework assumes a 10-year perspective. If the user's goal is short-term swing trading, this skill does not apply.
Failure modes the author warns about in the book
- Gambler-style break-even mentality: After being "trapped," comforting oneself with "long-term investing" — Duan Yongping explicitly says, "Many people often only think of the long term when they are trapped." This is not opportunity cost thinking, but a disguise for the sunk cost trap.
- The illusion of "persistence": "If you still feel like you are 'persisting,' then you are not yet a value investor" — needing to "persist" shows that deep down you do not truly agree, and the opportunity cost framework cannot save you.
- Frequent re-examination leads to speculation: Duan Yongping reminds us that holding = buying does not mean "thinking every moment about whether it is overvalued." Excessive attention to the market instead turns into speculation. The correct use is to review occasionally (when there is new capital, when a new target is found), not to watch the market every day.
The author's blind spots / limitations of the era
- The framework assumes investors can clearly judge "the best alternative" — in reality, the boundaries of the circle of competence are blurry, and many investors overestimate their understanding of the alternatives.
- Differences in capital size: Duan Yongping's large-capital operations (such as "add to positions when there is cash flow") may not be optimal for small capital; small capital may face higher opportunity costs.
- Taxes and transaction costs are ignored in the "holding = buying" equation — frequently adjusting positions according to this logic may generate substantial taxes and fees.
Adjacent methodologies that are easy to confuse
- Take-profit and stop-loss discipline: Superficially similar (both decide when to sell), but take-profit and stop-loss are anchored to price/percentage, while opportunity cost is anchored to value comparison; the logic of the two is completely opposite.
- The "buy more as it falls" averaging-down strategy: Duan Yongping explicitly opposes "adding to the position because the earlier purchase lost money and you want to lower the average cost" — this is not opportunity cost thinking, but the sunk cost trap.
Related skills (to be filled in stage 3)
- depends-on: [ownership-mindset, dcf-valuation]
- contrasts-with: []
- composes-with: [equanimity-mindset]
Audit information
- Verification passed: V1 cross-domain / V2 predictive-power / V3 exclusivity
- Test pass rate: Pending stage 4
- Distillation time: 2026-04-16