Why ₩100 today ≠ ₩100 next year
Hand someone ₩100 right now, they get ₩100. Ask them to wait a year for that same ₩100. They'd rather not. Why?
Because of what they could have done with that ₩100 in the meantime. Put it in a savings account at 5% — by next year it'd be ₩105. Bought a coffee — they'd have had the energy. Bought a stock — could be ₩120 by year-end. Anything they could have done with the ₩100 over the year, they couldn't do because they were waiting.
That "anything they could have done" is called opportunity cost. The cost of waiting is whatever else you could have used the money for. And here's the kicker: that cost isn't zero, even if all you'd have done is leave it in a savings account. Saving counts. Investing counts. The point isn't the specific path — waiting itself has a cost.
The picture: the timeline
Picture a horizontal line — the timeline. Left end is today. Right end is some future year. Money sitting at any point on that line has a value. Same nominal amount, but different actual value depending on where on the line it sits.
₩100 at the right end (next year) is worth less to you than ₩100 at the left end (today). How much less? Depends on what you could have done in the meantime — i.e., the prevailing interest rate. At 5%, ₩100 next year is worth about ₩95.24 today. At 10%, it's worth about ₩90.91 today. Lower rate, smaller penalty for waiting; higher rate, bigger penalty.
That "shrinking back to today" is called discounting. The interest rate (or whatever rate captures opportunity cost) is the discount rate. We'll use the letter r for it from here on. r shows up in every finance equation. Now you know what it actually represents — opportunity cost wearing a Greek-letter outfit.
Why this is the foundation of everything that follows
Bond prices? Discounted cash flows. Stock valuation? Discounted cash flows. Mortgage payments? Discounted cash flows. Insurance premiums, retirement projections, M&A acquisition values, private equity returns — all built on discounting future money to today.
And the reason discounting works is exactly this lesson: future money is worth less than today's money. Time has a price. The rest of finance is elaborating on this one idea.
So when Track 6 hits stock valuation and we use P = FCF / (r - g), the r in there is opportunity cost. The FCF / (1+r)^t in DCF? Discounting cash flow back to today. The (1+r)^n in compound interest? Forward-projecting today's money. Same idea, different direction.
Inflation is a sibling of this
Even if you had zero opportunity to invest, inflation alone would make ₩100 next year worth less than ₩100 today (a coffee next year costs more than a coffee today). So opportunity cost and inflation both push the same way: future money buys less. The math treats them the same — both are reasons to discount.
We'll come back to nominal vs. real (inflation-adjusted) returns in Track 4. Right now, just lock in: future money is worth less. Period.
시간의 가격과 기회비용의 원리를 은퇴 자산 설계에 도입해 이해를 한다. 일반적인 저축이나 민간 보험은 표면적인 명목가치(Nominal Value)를 보장하지만, 시간이 흐를수록 물가 상승이라는 공격에 노출되어 가치가 훗날 손에 쥐는 쭈글이 사과와 같다. 그러나 국민연금 시스템에는 국가가 직접 관리하는 강력한 가치 복원 장치가 있다. 시간이 흐름에 따라 미래의 돈이 작아지는 TVM(화폐의 시간 가치)의 페널티를 제도가 직접 상쇄해 준다. 미래의 현금흐름을 현재가치(PV)로 환산할 때 가치가 훼손되지 않도록 싱싱한 사과를 유지해 준다. 국민연금이 TVM의 페널티를 제도적으로 상쇄하며 실질 구매력을 보장해주는점은 시간의 가격을 이겨내는 금융 전략이다.