Ideas & Opportunity

Two of us disagree on how big the opportunity is. How do we resolve a market-size argument between cofounders?

A starting point

Stop arguing about the number and get specific about the assumptions behind it, because you're almost always disagreeing about who the customer is, what they'd pay, or how fast the market grows, not the arithmetic. Write both models side by side, name the two or three assumptions where you differ most, then design the cheapest test that would move one of you. As a starting point, a disagreement you can turn into a testable question is healthy; one that stays about vibes will quietly poison the partnership.

Go deeper

Hand-picked from around the web, each with a note on why it earns your time.

3 resources 2 link-checked Listen Read Use

Listen

🎧 Podcast
Free Intermediate

Why we picked it A market-size fight is rarely just about the numbers, it is often power, recognition, and who gets the final say wearing a spreadsheet as a costume. Psychologist Matt Jones, who works with founding teams and wrote The Cofounder Effect, walks through how to have the disagreement without damaging the relationship: contain the conflict, use non-blaming language, and translate the operational dispute into what is really going on underneath. Listen to this before your next hard conversation so the argument stays about the market and not about each other.

Why Startups Fail Due to Co-Founder Conflict and How to Fix It (with psychologist Matt Jones)

On The Startup CEO Show by Mark MacLeod (host), Matt Jones (guest) ~45 min

  • Roughly two thirds of promising startups fail from cofounder conflict, so treating disagreement as a skill to practice is not soft, it is survival.
  • Contain the conflict (scheduled time, private, non-accusatory language) so a single argument does not spill into your execution.
  • Regular cofounder check-ins on how the partnership itself is working prevent small disagreements from hardening into resentment.
Open markmacleod.me →

Read

📄 Article
✓ Link checked Free Beginner

Why we picked it When two cofounders disagree on how big the market is, the fastest way out is to stop arguing opinions and turn the disagreement into a test. Elliot Shmukler's framework here does exactly that: instead of one of you overruling the other, you write down what each side believes, design a cheap experiment, and let the data settle it. That reframes a market-size fight from who is more persuasive into what is actually true, which is the only version of the argument worth having.

The 6 Decision-Making Frameworks That Help Startup Leaders Tackle Tough Calls

From First Round Review by First Round Review (featuring Elliot Shmukler) ~12 min read

  • A disagreement is usually two different assumptions about reality, so name each side's assumption before you debate the conclusion.
  • Replace the verdict from whoever is more senior with a small experiment, then let the result decide, which keeps both cofounders bought in.
  • This is one of six framings in the piece, so you also pick up other lenses (reversible vs irreversible calls) for the decisions you cannot test.
Open review.firstround.com →

Use

📋 Template
✓ Link checked Free Beginner

Why we picked it The Test Card is a one-page worksheet that forces a vague market-size belief into four fields: what we believe, how we will test it, what we will measure, and what result would prove us right. Fill one out for each cofounder's version of the market and the disagreement stops being a debate and becomes two experiments with clear pass or fail bars. It is free, widely used, and takes minutes to complete, so there is no excuse to keep arguing in the abstract.

Test Card

From Strategyzer by Strategyzer (Alexander Osterwalder) one-page worksheet

  • It converts a differing assumption into a hypothesis plus a concrete metric and a success threshold, so you both agree in advance on what would change your mind.
  • Writing each cofounder's belief on a separate card surfaces exactly where the two of you actually diverge.
  • Pair it with the companion Learning Card to record what the test showed, so the decision is documented, not relitigated later.
Open strategyzer.com →

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