📖 Book
✓ Link checked
Paid
Beginner
Why we picked it
The single best thing ever written on customer conversations. It teaches you to ask about the customer's life and past behaviour, not your idea, so you can't be lied to. If a founder reads one thing before talking to a single customer, it's this.
From
momtestbook.com
by Rob Fitzpatrick
~130 pages
- Talk about their life, not your idea.
- Ask about specifics in the past, not opinions about the future.
- 'That's so cool, I'd totally buy it' is a compliment, not data, dig for commitment and evidence.
Open
momtestbook.com →
✍️ Essay
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Free
Intermediate
Why we picked it
Most market sizing advice online is generic TAM SAM SOM filler. This one is written by an investor, backed by a survey of 30 VCs, and it is honest about the thing that matters: a big number pulled from an industry report proves nothing. It walks you through building the number bottom up (customers times what they pay you per year), which forces you to confront whether real people will actually pay, and that is the honest test of whether an idea can grow past a niche.
From
Pear VC
by Ian Taylor
~15 min read
- Size the market bottom up (count of real customers times annual revenue per customer), not by claiming a percent of some giant top down figure.
- TAM, SAM, and SOM are used loosely across the industry, so state your assumptions plainly instead of hiding behind the acronyms.
- Project the market out five or more years and include how you would actually reach and acquire customers, since a market you cannot serve is not your market.
Open
pear.vc →
✍️ Essay
✓ Link checked
Free
Intermediate
Why we picked it
When there is no category report to point at, you have to build the number yourself, and this is the essay that teaches you how. It walks through bottoms-up sizing (start from your actual customer, their willingness to pay, and how you will reach them) and shows why the top-down 'we just need 1 percent of a huge market' story falls apart. Treat it as the method for a defensible estimate, not a promise about how big you will get.
From
Andreessen Horowitz
by Anu Hariharan, Frank Chen, Jeff Jordan
~20 min read
- Build TAM from the bottom up: real customer profile times realistic price times how many you can actually reach and sell to.
- Top-down percentages inflate the number and hide the hard part, which is distribution and go to market.
- Some of the best companies (eBay, Airbnb) started against a market that looked small, then expanded the use case, so a modest starting number is not a dealbreaker.
Open
a16z.com →
📄 Article
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Free
Intermediate
Why we picked it
This is the most direct answer to your question from an investor who reads these slides for a living. It walks through why a bottoms-up number (customers times price they will pay) signals you understand your buyer, and treats the classic top-down TAM slide as a trap. You get a concrete formula and worked examples you can drop straight into your deck.
From
Underscore VC (Richard Dulude)
by Richard Dulude
12 min read
- Bottoms-up market size equals number of customers times price they will pay
- A bottoms-up slide signals you actually know your buyer and pricing
- Lead with bottoms-up and use the big top-down figure only as context
Open
underscore.vc →
✍️ Essay
✓ Link checked
Free
Beginner
Why we picked it
This is the essay that forces the honest question underneath your idea: are you building a growth company or a good small business, because they are different DNA and require different lives. Graham is blunt that a barbershop is not a startup no matter how new it is, and that clarity helps you choose on purpose instead of drifting. There is nothing wrong with either path, but you should pick the one you actually want before you spend years on it.
From
Paul Graham
by Paul Graham
~20 min read
- A startup is defined by fast growth, not by being new or funded, so a business that cannot grow fast is a different (and often fine) choice, just not a startup.
- Growth needs two things at once: something many people want, and a way to reach them at scale, if either is missing the idea caps out as a niche.
- Deciding whether your idea can grow beyond a niche is really deciding what kind of company, and what kind of years, you are signing up for.
Open
paulgraham.com →
✍️ Essay
✓ Link checked
Free
Beginner
Why we picked it
The definitive essay on where good ideas come from: notice problems you personally have, don't force it. Use it as the lens for judging whether your idea is a real problem or a solution in search of one.
From
paulgraham.com
by Paul Graham
~20 min read
- Live in the future and build what's missing.
- The best ideas look like bad ideas at first (schleps and hard-to-explain).
- Start with problems you have, in a domain you actually know.
Open
paulgraham.com →
📄 Article
✓ Link checked
Freemium
Intermediate
Why we picked it
Consumer PMF advice does not map cleanly onto B2B, where deals are few, considered, and slow, which describes many Indian startups selling to businesses. This guide covers the specific signals that matter when you have ten design partners instead of ten thousand users. Read it if the 40 percent survey feels awkward for your low-volume, high-value product.
From
Lenny's Newsletter
by Lenny Rachitsky
~3,000 words
- In B2B, renewal and expansion are your retention signal, not daily use
- A handful of paying, referring customers can confirm fit
- Watch whether sales gets easier and cycles get shorter over time
Open
lennysnewsletter.com →
📖 Book
✓ Link checked
Paid
Intermediate
Why we picked it
Savoia, a former Google innovation lead, argues most ideas fail because they were never 'the right it', and he gives you cheap pretotypes (fake doors, mechanical turks, one-night stands) to get real demand data in days. Instead of asking people if they would use it, you watch whether they actually act. This is how you catch a nice-to-have before you spend a year on it.
From
Alberto Savoia
by Alberto Savoia
256 pages
- Collect your own data on whether people will actually act, not just say yes
- Pretotypes test demand in days for pennies before you build anything
- Most ideas fail because the market did not want it, so test that first
Open
albertosavoia.com →
📄 Article
✓ Link checked
Free
Beginner
Why we picked it
A practical walkthrough of reading Reddit communities as a free market signal, including how to pick the right subreddits and what their size does and does not tell you. It pairs well with counting people in groups, and it is honest about the limits so you do not over read a small sample. Good grounding before you treat community counts as proxies.
From
ZoomInfo
by ZoomInfo
12 min read
- A niche 50k community can beat a noisy 500k one
- Read repeated questions as built in demand signals
- Use communities for qualitative signal, not hard totals
Open
pipeline.zoominfo.com →
📄 Article
✓ Link checked
India
Free
Intermediate
Why we picked it
Blume's annual report is the single best data-grounded read on what is actually happening in Indian internet and consumption, not what is trending on VC Twitter in San Francisco. It shows you adoption curves (UPI, quick commerce, ONDC, how few households actually shop online) so you can pressure-test whether a hyped trend has the demand base to land here. Treat it as a starting map of Indian reality, then judge your specific trend against it.
From
Blume Ventures
by Sajith Pai, Anurag Pagaria and team (Blume Ventures)
~180 charts
- Grounds trend-spotting in real Indian adoption data (income distribution, online-shopping penetration, UPI-native monetization) instead of imported hype.
- Indian startups are building a distinct playbook (micro-subscriptions on UPI Autopay, DPI rails) that has no clean US analogue, so copying a US trend directly often misses the real opportunity.
- A trend can be huge in raw numbers yet thin in monetizable demand: the report repeatedly separates users from paying users.
Open
blume.vc →
