The TAM Inflation Trap — Revisiting Crossing the Chasm

#Why Founders Inflate TAM

Founders usually inflate TAM (total addressable market) for one of three reasons. First, a vague belief that “a big number looks good.” Second, a comparison instinct after seeing other business plans — “I guess you need to write something this big to pass.” Third, it's an expression of their own confidence. But reviewers and investors see hundreds of business plans every year. An inflated TAM gets caught on page one.

#Crossing the Chasm — The 5–15% Early Adopter Rule

Geoffrey Moore's Crossing the Chasm (1991/2014) covers the technology adoption lifecycle. A new technology product never captures the whole market at once. Adoption spreads in order — Innovators (2.5%) → Early Adopters (13.5%) → Early Majority (34%) → Late Majority (34%) → Laggards (16%) — and there's a “chasm” between Early Adopters and the Early Majority.

#Separating TAM/SAM/SOM — Consistency of Source and Units

TAM/SAM/SOM are defined as follows. TAM = the total market if every potential customer adopted your solution at 100%. SAM = the market reachable given your business model and geography. SOM = the market you can realistically capture within the next 3–5 years. What matters about these three numbers isn't their absolute size — it's how they relate to each other.

Note: the figures in the table above are illustrative, meant to show the format. When you actually write your business plan, you need to look up and cite the latest data yourself from primary sources like Statistics Korea, KOSIS, or Statista. Copying an unverified source as-is will cost you credibility immediately during review.

Units and timeframes must always match. If TAM is in global USD but SAM is in Korean won, you lose credibility instantly. If TAM is 2024 data but SOM is a 2030 projection, the numbers aren't comparable. Every figure needs to be aligned to the same currency, the same point in time, and the same definition.

#5 Inflation Patterns — Mistakes That Get Caught Immediately

1. Top-down only — the “if we capture X% of the global market, that's ₩___” format. No bottom-up formula means automatic suspicion.
2. Mixed units — TAM in dollars, SAM in won, SOM in euros. No stated exchange-rate date, either.
3. Unnamed source — stops at “according to a market research firm” without naming which firm or what year.
4. Inconsistent timeframes — TAM as of 2025, SAM projected to 2028, SOM targeted for 2030. The timeline doesn't line up.
5. Ignoring competitors — combined competitor revenue is 60% of TAM, yet the SOM you're claiming is bigger than that.

#How to Write Market Size People Trust — Bottom-Up + Why Now

A market size that's both honest and compelling comes from presenting three things together: a bottom-up formula, credible sources, and Why Now. A small number backed by solid logic is rated far more highly than a big one that isn't.

State 3–4 core assumptions in your bottom-up estimate: “price is assumed at ₩___,” “conversion rate applies the industry average of __%,” “customer count is based on the ___ survey,” and so on. When assumptions are stated explicitly, a reviewer can check the math themselves — and numbers that can be checked earn trust.

#Self-Diagnosis Checklist for Market Sizing in Your Business Plan

1. Are TAM/SAM/SOM presented as three separate layers? (A single number reads as low credibility.)
2. Do units, timeframe, and currency all match? (Any mismatch is an instant deduction.)
3. If TAM is global but SAM narrows to Korea, is the reasoning for that narrowing clear?
4. Does SAM fall within 5–15% of TAM? (The Crossing the Chasm rule)
5. Does SOM include a bottom-up formula (customer count × price × conversion rate)?
6. Is the source labeled as government, a public agency, or tier-1 market research?
7. Does it address at least 2 of the 3 Why Now elements (regulation, technology, behavior change)?
8. Does SOM avoid conflicting with combined competitor revenue?