The total addressable market (TAM) is often treated as the holy grail of early-stage investing. Slide decks flaunt massive TAMs like “a $50 billion industry ripe for disruption!” as if that alone justifies an investment. But for seed-stage investors obsessing over TAM is not just a mistake; it’s a fallacy.
Why? Because the best startups don’t just capture a share of an existing market, they redefine or even create entirely new markets. And at the seed stage business models are still fluid, pivoting based on customer feedback, market conditions and execution realities. Investing in a startup because it targets a large TAM today often ignores the fundamental truth of how great companies are built.
Startups Change Business Models. A Lot
The reality is that most early-stage startups will shift their business model multiple times before they find product-market fit. Founders start with an initial hypothesis, but as they engage with customers they refine their approach, often expanding into unexpected areas.
Take Slack for example. It started as an internal tool for a gaming company but pivoted into enterprise communication. Or Shopify, which began as an online snowboard store before realizing the real opportunity lay in powering e-commerce for others. Had investors assessed them purely on their original TAMs they might have dismissed them entirely, which many investors did.
Great founders aren’t just looking at TAM slides; they’re figuring out how to build something great regardless.
The Best Startups Create Their Own TAM
Consider Uber. In its early days the concept of “ride-hailing” was small, mostly black car services in major cities. A traditional investor might have balked at the limited TAM of private drivers. But Uber didn’t just take a slice of an existing market; it created an entirely new one by onboarding everyday drivers and redefining urban mobility.
Similarly, Airbnb wasn’t just competing in the hotel industry; it unlocked supply that didn’t previously exist, growing the market beyond what traditional TAM analysis could predict. If you had looked at the size of the couch-surfing market in 2008 you’d have laughed off the idea of a billion-dollar business. And yet here we are.
What Seed Investors Should Focus On Instead
So if TAM is unreliable at the seed stage what should investors focus on? Here are a few better indicators:
- Founder Insight: Is the team identifying a problem that others have overlooked? Are they obsessed with solving it?
- Early Traction & Customer Behavior: Even if the initial market seems small, are users engaging deeply? Are they coming back?
- Market Expansion Potential: Can the startup evolve its offering to redefine its market? Are there adjacent opportunities it can tap into?
- Execution & Adaptability: Given that pivots are almost inevitable, does the team show resilience and adaptability?
The best seed-stage startups don’t fit neatly into existing TAM models. They start with a wedge, a narrow but highly engaged market, before expanding into something far bigger than anyone initially imagined. That’s what makes early-stage investing so exciting and unpredictable.
Don’t Dwell on TAM
Relying on TAM at the seed stage is like judging a book by its unfinished first chapter. The best founders don’t just play within existing markets—they invent new ones. Instead of fixating on today’s market size, seed investors should back teams with the vision, adaptability and execution chops to create their own TAM. Because in the end the real question isn’t “How big is the market today?”, it’s “How big could it be if this startup succeeds?”