Psychology & Behavior
ProSunk Cost Check
沉沒成本檢查 · Source: Richard Thaler / Daniel Kahneman
Detecting whether you're continuing something you shouldn't — because of what you've already invested
Core Concept
The sunk cost fallacy: continuing to invest because of what you've already spent — even when rational analysis says stop. "I've already put so much into this" is a dangerous rationale. Past costs are irrecoverable. The only thing that matters is future expected value.
✓ When to use this
When you consider continuing because "I have already invested so much." For projects, relationships, degrees, investments — time and money already spent are past tense, irrelevant to whether continuing is worthwhile now.
✗ When not to use this
Near-completion situations where remaining cost is less than completion value — continuing is rational, not a sunk-cost trap. Also unsuitable for relationships or moral commitments where commitment ethics matters, not pure accounting.
Questions you will be asked
Using this framework, you will work through —
- 1.What are you considering whether to continue?
- 2.What have you already invested? (Time, money, emotion, opportunity cost)
- 3.Key question: If you were encountering this opportunity for the first time today, would you choose to invest?
- …and 3 more
Worked example
Expand to see what a filled-in run looks like
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Worked example
Expand to see what a filled-in run looks like
Situation
Side project 做了 18 個月，月收入只有 3 萬元、用戶成長停滯。每次想停就覺得「都做這麼久了」。最近接到正職邀約，逼我必須做選擇。
1. What are you considering whether to continue?
是否該停掉這個 side project，去接正職。
2. What have you already invested? (Time, money, emotion, opportunity cost)
已投入：18 個月晚上 + 假日、約 200 個工作天的精力、$80k 投入廣告和工具、放棄了一些社交與運動時間。
3. Key question: If you were encountering this opportunity for the first time today, would you choose to invest?
已投入的不能拿回來——它是過去式。問題不是「值不值得停」，是「從今天起接下來 6 個月，繼續 vs 不繼續，哪個收益更大？」
4. What are the expected future benefits of continuing?
從零開始假設：如果今天是第一次看到這個 project（3 萬月入、停滯成長、看不出突破點）——我會投入嗎？答案是「不會」。
5. If you stop, what could you do with the freed resources?
理性繼續理由：什麼都沒有。情緒繼續理由：「太可惜」、「再撐撐看」、「怕被認為失敗」——全是沉沒成本與面子。
6. Continue or stop? How much of this decision is based on the future vs. the past?
停掉。把 18 個月的學習與認知當作下一個 project（或正職）的資產。寫一篇回顧文，正式跟 project 告別。
Use it inside ChatGPT / Claude
Paste the prompt below and the AI will walk you through this framework, one question at a time.
你現在是引導使用者檢測「沉沒成本陷阱」的教練。 依序問： 1) 你正在考慮繼續還是停掉什麼？ 2) 至今已投入了什麼？（金額、時間、精力、機會） 3) 提醒：這些是沉沒成本，已經不可回收——跟「現在繼續是否划算」應該無關。 4) 從零開始假設：如果今天是第一次看到這個機會（不知道你已投入），你會投入嗎？ 5) 你想繼續的理由——多少是基於未來預期值，多少是「太可惜」、「面子」、「不想認輸」？ 6) 排除沉沒成本後，你的決策是什麼？ 提醒：「都已經 X 個月/萬元/年了」這個句型如果出現，就是沉沒成本在說話。 互動規則： 1. 一次只問一題，等使用者回答後再進入下一題。 2. 使用者答完所有題目前，不要做總結或下結論。 3. 若答案太抽象、太籠統，請追問一次具體例子或數字後再繼續。 4. 全部答完後，輸出三段：(a) 摘要使用者的關鍵判斷；(b) 你看到的盲點或張力；(c) 一個具體下一步行動建議。 5. 不要替使用者做決定，只把判斷攤開讓他自己決定。
Related Frameworks
Investment & Finance
Commitment Escalation Check
Detecting whether you're escalating commitment to a failing bet — justified only by "I've invested too much"
Investment & Finance
Opportunity Cost Framework
Resource allocation decisions — how to deploy time, money, attention; especially when you're treating "do nothing" as a free option
Psychology & Behavior
Loss Aversion Check
Distinguishing between genuine risk assessment and your brain's irrational fear of loss
FAQ
How is the sunk cost check different from the commitment escalation check?
Sunk cost is "I won't stop because I've already invested" — refusing to exit; commitment escalation is its evolved form, "I'll double down to save what I've invested" — betting bigger and bigger. The latter is more dangerous because each additional bet raises the psychological cost of quitting, locking you in deeper.
How do I distinguish perseverance from the sunk cost fallacy?
Ask the key question: "If I were starting from zero today, would I still choose to continue?" If yes, that's reasonable perseverance based on future value, not a fallacy; if your main reason is "I've already put in so much," sunk cost is holding you hostage. The test: are you citing future value, or past cost?
How do I avoid falling into sunk cost again?
The most effective is pre-committed stop-loss conditions: while still calm and not emotionally invested, write down a clear "exit if X happens" rule. When the situation actually arrives, you don't re-decide in the moment — you just execute the pre-written rule. Also practice treating what's spent as nonexistent, resetting each time to a "zero-base decision today."
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