Why serviceable addressable market (SAM) matters to a first-time founder
Investors use your serviceable market to judge whether you understand who you can actually sell to today. Quoting only the huge total market suggests you have not thought about language, geography, price or sales channel. A realistic figure also tells you how much growth is available before you need a new product, a new country or a new way of selling, which shapes hiring and fundraising plans.
Examples of serviceable addressable market (SAM)
The ceiling might be every freelancer. You sell in English, at £20 a month, through a self-serve page, to people who invoice from the UK. That slice is the market you can serve. A German agency that needs a sales visit and a local bank transfer is in the ceiling and outside this slice.
Common misunderstanding
People use it as a second, slightly smaller version of the total market, with the same optimism. Or they confuse it with the share they will win. Reachable is not the same as won. The obtainable market is the near-term share of this slice.
When to use it
Define it when a total-market number is too large to aim at. If your current product and channel could not serve a group, leave them out, even if they would look good in the story.