Sunk Cost
Money already spent shouldn’t affect your decisions today
📌 Concept Explanation
Sunk Cost = Costs that have already been incurred and cannot be recovered; they should not become reasons for continued investment.
You bought a movie ticket, entered the theater, and found the movie terrible. Would you sit through it just because “the ticket money’s already spent”? The rational approach: the ticket cost is already sunk—whether you leave or not, it won’t come back. Continuing to sit there only wastes more of your time. Investing is the same—your purchase price is a sunk cost; it shouldn’t affect today’s judgment about “whether this stock is worth continuing to hold.”
💡 Core Understanding
1. Sunk cost is the most common psychological trap in investing, directly causing “holding on as losses mount.”
After most people get trapped in a position, they wait there for “breaking even” rather than calmly comparing which has greater opportunity: “continue holding” or “switch to something else.” This is sunk cost at work—the purchase price becomes a psychological anchor, preventing rational sell logic judgment. Duan says over 95% of people struggle with this most of the time.
2. Each day’s closing price is your opportunity cost; not selling equals buying again today.
This is the most powerful perspective for understanding sunk costs: you’re holding this stock today not because of what you paid for it originally, but because today you choose to continue holding it rather than switching to something better. This integrates with opportunity cost—your purchase price is irrelevant to today’s decision; today’s decision relates only to “this stock’s future value.”
3. Once you truly understand sunk cost, you can achieve “forget the purchase price, view the company’s value with ordinary mindset.”
Duan says this is the hardest hurdle. When you discover you bought wrong, sell immediately—don’t comfort yourself with “wait for breakeven.” The core of error and correction lies here: the cost of admitting error is far less than the cost of continuing to hold onto an erroneous decision. The spirit of Stop Doing List also lies here: once you discover it’s a pit, stop digging.
🛠 How to Practice
Whenever facing a position decision, ask yourself this question:
“If I had cash in hand today, would I buy this stock?”
If the answer is “no,” then your only reason for continuing to hold is sunk cost—you don’t want to admit the loss. At that point, the correct action is to sell, not wait.
Three signals that indicate you’ve fallen into the sunk cost trap:
- You say “I’ll wait for it to recover before selling”—this is sunk cost thinking
- You say “I’ve lost so much already, a little more doesn’t matter”—this is sunk cost thinking
- You say “I’m a long-term investor” but your original buy logic no longer holds—this is also sunk cost thinking
❓ Selected Q&A
Q: Mr. Duan, Munger says “we won’t sell a company just because it’s in trouble,” while Buffett says “if it’s a pit, stop digging.” Can these two principles apply to the same company? I’m still conflicted about past sunk costs.
A: If it’s the right company, you shouldn’t sell when it’s cheap. If it’s the wrong company, at least stop buying more. If you feel the company you currently hold will collapse someday in the foreseeable future, do you think you should: 1. Add to your position because previous purchases lost money, trying to average down and sell when it bounces to recoup costs? 2. Don’t buy but don’t sell either, hoping for a bounce opportunity to exit? 3. Forget what price you bought at and think with ordinary mindset about what this company is actually worth? …This last one is hardest.
Source: Duan Yongping Investment Q&A (Investment Logic Chapter), 2013-04-08
⚠️ Common Misconceptions
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❌ “If you lose money, wait for breakeven—otherwise it’s a real loss” — Correction: Duan says there’s a term in finance called sunk cost. If you truly understand it, you can resolve this question. Losses don’t “become real” at the moment of sale—they occurred the moment you made the wrong purchase. (Source: Duan Yongping Investment Q&A (Investment Logic Chapter), 2013-12-28)
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❌ “Averaging down is rational operation” — Correction: If the company itself is wrong, averaging down is just digging deeper in a hole. What Munger calls “stop digging” addresses precisely this situation. (Source: Duan Yongping Investment Q&A (Investment Logic Chapter), 2012-06-26)
💬 Original Quotes
“There’s a term in finance called sunk cost (also called sunken cost). If you truly understand it, you can answer your own question. I think over 95% of people struggle with this most of the time.” (Source: Duan Yongping Investment Q&A (Investment Logic Chapter), 2013-12-28)
“Sunk cost refers to costs that have resulted from past decisions and cannot be changed by any present or future decision. The story illustrates spending new investment trying to recover already-sunk money—the result was wasted expenditure.” (Source: Duan Yongping Investment Q&A (Investment Logic Chapter), 2010-03-30)
“Thinking of sunk cost. Also recalling what old Ba said: if it’s a pit, stop digging. Look at how many people are digging pits for themselves and you’ll understand.” (Source: Duan Yongping Investment Q&A (Investment Logic Chapter), 2012-06-26)
🔗 Related Nodes
Upstream Concepts (prerequisites for understanding this concept): Opportunity Cost · Ordinary Mindset
Downstream Concepts (conclusions derived from this): Sell Logic · Error and Correction · Stop Doing List
Related Figures Duan Yongping · Buffett · Munger
沉没成本
已经花出去的钱，不该影响你今天的决定
📌 概念解析
沉没成本 = 已经发生、无法收回的成本，不应该成为你继续投入的理由。
你买了一张电影票，进场后发现电影很烂。你会因为”票钱已经花了”而坚持看完吗？理性的做法是：票钱已经沉没了，不管你走不走都回不来了。继续坐在那里只是在浪费你的时间。投资也是一样——买入价格是沉没成本，它不应该影响你今天”这只股票值不值得继续持有”的判断。
💡 核心理解
1. 沉没成本是投资中最常见的心理陷阱，直接导致”越亏越拿”。
大多数人被套住之后，会守在那里等”解套”，而不是冷静比较”继续持有”和”换成其他标的”哪个机会更大。这就是沉没成本在作怪——买入价格成了心理锚点，让人无法做出理性的卖出逻辑判断。段永平说，95%以上的人大多数情况下会想不开。
2. 每天的收盘价就是你的机会成本，没有卖就等于今天重新买了一次。
这是理解沉没成本最有力的视角：你今天持有这只股票，不是因为你当初花了多少钱买的，而是因为你今天选择继续持有它，而不是换成其他更好的标的。这和机会成本是一体的——你的买入价格与今天的决策无关，今天的决策只和”这只股票未来的价值”有关。
3. 真正懂了沉没成本，就能做到”忘掉买入价，平常心看公司值多少钱”。
段永平说，这是最难的一关。发现买错了，要马上卖，而不是用”等解套”来安慰自己。错误与纠错的核心就在这里——承认错误的成本，远小于继续持有错误决策的成本。Stop Doing List的精神也在于此：发现是坑，就停止挖。
🛠 如何实践
每次面对持仓决策时，问自己这个问题：
“如果我今天手里拿的是现金，我会买这只股票吗？”
如果答案是”不会”，那你继续持有的唯一理由就是沉没成本——你不想承认亏损。这时候正确的做法是卖出，而不是等待。
判断是否陷入沉没成本陷阱的三个信号：
- 你说”等涨回来再卖”——这是沉没成本思维
- 你说”已经亏了这么多，再跌也无所谓了”——这是沉没成本思维
- 你说”我是长期投资者”，但买入逻辑早已不成立——这也是沉没成本思维
❓ 精选问答
问：请教段先生，“我们不会仅仅因为企业处于困境就卖掉它”（芒格）和”如果是个坑就别再往下挖了”（巴菲特），这两句话会适用在同一个公司吗？我还在过去的沉没成本中矛盾着。
答：如果是对的企业，就不应该在便宜的时候卖掉。如果是错的公司，至少不要再买了。如果你觉得自己现在持有的公司在看得到的未来某一天会完蛋，你觉得是应该：1. 加码，因为前面买的亏了，要摊低成本等他反弹时卖掉补回成本？2. 不买但也不卖，希望能有个反弹的机会卖掉？3. 忘掉自己什么价买的，平常心去想这个公司值多少钱？……这个最难。
来源：段永平投资问答录(投资逻辑篇)，2013-04-08
⚠️ 常见误区
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❌ “亏了就要等解套，不然就是真亏了” — 正解：段永平说，财务上有个名词叫沉没成本，如果你真懂了，你就能解答这个问题。亏损在卖出的那一刻并没有”变成真的”——它在你买错的那一刻就已经发生了。（来源：段永平投资问答录(投资逻辑篇)，2013-12-28）
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❌ “摊低成本是理性的操作” — 正解：如果公司本身是错的，摊低成本只是在一个坑里越挖越深。芒格说的”停止挖掘”，正是针对这种情况。（来源：段永平投资问答录(投资逻辑篇)，2012-06-26）
💬 原文金句
“财务上有个名词叫沉入成本，也有叫沉没成本的，如果你真懂了，你就能解答你的问题。我认为95%以上的人大多数情况下会想不开的。“（来源：段永平投资问答录(投资逻辑篇)，2013-12-28）
“沉入成本是指由于过去的决策已经发生了的，而不能由现在或将来的任何决策改变的成本。故事讲的就是为了去救已经沉没的钱又花了新的投资，结果是白花了。“（来源：段永平投资问答录(投资逻辑篇)，2010-03-30）
“想起沉入成本。还想起老巴说的，如果是个坑就别再往下挖了。看看有多少人在给自己挖坑就明白了。“（来源：段永平投资问答录(投资逻辑篇)，2012-06-26）
🔗 关联节点
下游概念（由此推导出的结论）： 卖出逻辑 · 错误与纠错 · Stop Doing List