Total Addressable Market (TAM)vsProduct-Market Fit (PMF)

Total Addressable Market is the total revenue opportunity for your product if you achieved 100% market share. It's broken into three layers: TAM (total market), SAM (Serviceable Addressable Market — the segment you can reach), and SOM (Serviceable Obtainable Market — what you can realistically capture). Investors use TAM to assess if a market is worth entering. VCs typically want a $1B+ TAM to justify their fund economics.

Product-Market Fit is the degree to which your product satisfies a strong market demand. When you have PMF, customers are actively pulling your product from you rather than you pushing it onto them. Marc Andreessen defined it as 'being in a good market with a product that can satisfy that market.' The Sean Ellis test quantifies it: if 40%+ of users say they'd be 'very disappointed' without your product, you have PMF. Before PMF, nothing else matters — marketing spend is wasted, hiring is premature, and features are guesses. After PMF, everything gets easier: organic growth appears, retention improves, and word-of-mouth starts compounding.

The most common TAM mistake is 'top-down' sizing that inflates the number. Saying 'the global CRM market is $80B, so our TAM is $80B' is nonsensical if you only sell to 500-person tech companies in North America. This 'TAM fantasy' is the #1 reason investor pitches fail — it signals the founder doesn't understand their actual market.

Founders declare PMF too early based on vanity metrics — sign-ups, press coverage, 'exciting conversations' with potential customers. True PMF means users would be genuinely disappointed if your product disappeared. The second trap: assuming PMF is binary and permanent. PMF exists on a spectrum and can erode as markets shift (Blackberry had PMF until iPhone changed the market). Also: PMF for one segment doesn't mean PMF for another — you might have PMF with startups but not enterprises.

Use bottom-up TAM calculation: count the number of potential customers you could serve × what they'd pay annually. Start with SOM (what you can realistically get in 3 years), then SAM, then TAM. Be specific: '12,000 mid-market SaaS companies × $30K/year ACV = $360M SAM.' VCs respect founders who demonstrate precise market understanding over inflated claims.

Run the Sean Ellis survey: ask existing users 'How would you feel if you could no longer use [product]?' with options: Very Disappointed, Somewhat Disappointed, Not Disappointed. If 40%+ say 'Very Disappointed,' you likely have PMF. If not, interview the disappointed users to learn what they love, and double down on that specific value. Track the PMF score quarterly — it should improve as you refine the product.