The market decision your other go-to-market decisions depend on.

The headpin itself: TAM, SAM and SOM, built from the bottom up

Bottom up means from accounts, not from an analyst's total. Demarcate the characteristics that define a segment and that exist as real filters in a real data source: revenue, employee count, store count, geography, industry. Filter every account inside your total market, use a proxy you can defend for each one's revenue potential, add growth for a multi-year view, and sum it. That is the TAM, and it is the number investors need.

Then narrow. The SAM is the set of segments your current means give you a right to win in, defined by more granular filters. That narrowing is the workshop half. It runs on tribal knowledge currently distributed across six people's heads, which is why it is built with your team rather than delivered to them, and it is the number that focuses investment.

Then decide what share of each SAM you can actually take in a year, and whether you have the spend and the people to take it. That is the SOM, and it is the number the field works from. It focuses field activity, and campaigns and territory assignments get organized around it. It is also the data your ideal customer profile gets honed from, which is the section after next.

Analyst figures are worth having as a benchmark against your own answer rather than as a substitute for it. In my own note on this method I called the top down version suspect for execution and important for investor validation and credibility, and I would say both halves again. A market figure from IHL, Forrester or Gartner tells you whether your bottom up number is sane. It will not hand your CRO a single account.

What finance can set once this exists

A revenue budget derived as a share of the market you intend to capture rather than as an increment on last year. Quota and selling headcount cascading from it. The pipeline coverage it takes to make that quota, counted rather than assumed. A cost budget related to that revenue budget rather than negotiated against it. Capacity planning across sales, sales engineering, support and implementation, with ramp counted honestly.

When I have assigned ownership of this work, I have assigned it to Finance, with marketing, product, IT and sales leadership participating. Marketing usually builds the slides. Finance has to own the number, because Finance is the function that has to live inside it.

What product can build against once this exists

This is the half that gets left out, and leaving it out is how a roadmap ends up funded against a market nobody ever agreed on. The same segmentation that lets finance set a number lets product invest in offerings aligned to it.

For each SAM segment, a stated problem and the value of solving it, quantified wherever it can be. Then the specific use cases that make up the complete solution, each with its own value proposition and its own claim to being different. Four questions decide each one. Who is going to care enough to write a check, by industry and by title? Why will they care, tied to a number they are personally measured on? Why will they choose your capabilities over a competitor claiming to do a similar thing? Why will they believe you?

Beneath those use cases sit the features engineering builds. Above them sits everything that keeps go-to-market pointed at the right buyer and keeps your operations team from spending next year supporting unprofitable customers who were never aligned to the strategy. It is also why the product wants a reference implementation, tested against the market's use cases rather than against a feature list.

The segments you are not going after

This is the half of segmentation that gets skipped, and skipping it is what makes the whole exercise feel academic six weeks later. A model that tells you where to play and not where to stop has produced a picture rather than a decision. The debate you avoid in the workshop is the debate you then have in pipeline review instead, one deal at a time, with less information and more sunk cost in the room.

So the output carries a written attack or leave call for every segment, with the reasoning attached to both sides. The reasoning for the segments you leave is the part that gets re-litigated later, usually by whoever's plan depended on one of them.

An ideal customer profile tight enough to disqualify a deal

In order to say no to the wrong deals, you need a pipeline of the right ones. That is what the profile is for, and it is why it gets built at the end of this work rather than at the start.

It is honed from two inputs and both of them are yours. The first is the SOM data you have just built from the bottom up: real accounts, real filters, and a defensible view of what you can take. The second is your win and loss history, read for what it says about where you win, where you lose, and where you win and later wish you had not. A profile built from the first alone describes a market. A profile built from the second alone describes your past. Together they produce qualification robust enough to hold up in front of a seller who wants the deal.

Because that is the moment it earns its keep. A seller is on a call, the opportunity is real enough to be tempting, and something has to be able to tell him this is not one of ours. The test is not whether the profile is accurate. Plenty of accurate profiles have never disqualified anything. The test is whether it can say no to a deal somebody wants, in language he can carry into a live conversation.

And the bill for getting it wrong does not land on sales. It lands downstream, on the people who implement, support and renew an unprofitable customer who never fit the strategy.

Which is why I ask your Chief Customer Officer for retention and expansion history by segment before the room narrows anything. A segment that closes well and renews badly looks winnable right up until you fund it.

Built this way the profile does one more thing, and it is the thing that makes the rest of it hold: it aligns strategy and product with the field. The segments finance funded, the segments product is building for and the segments your sellers qualify against are the same segments, described the same way, because they came out of the same model.