You don't have a product until there's ~3 customers, with perspective to more. Before that you're essentially a consultant. I'll add that to the next version of the doc, too.

The point is: For anything you build, you can find 1 customer. It's only when there's multiple customers that like the product and want to improve it where you move from "consulting" or "custom development" to "product".

That comes down to the ability to say no (or at least "not yet"). I have seen lots of startups that land a few mid or big clients and lose the plot by serving every throwaway request the client makes. Doing this slowly turns your product into a bespoke solution not fit for others. There needs to be constant tension between the product goals and its application, and holding that line will always, always annoy a sizeable swath of users.

Apple famously ignored users on lots of fronts: can't manually add RAM, mouse has 1 button, etc. They didn't serve one type of user specifically so they could appeal to a larger market. You can't serve everyone.

This rings true. A previous job I had did email analytics for the investment banking industry (from boutique firms up to the largest banks in the world). I kid you not, the single biggest driver of our success was the simple fact that our expertise in email meant that we fixed problems that almost all these firms had with email deliverability (bad IPs, SPF/DKIM/DMARC, broken unsubscribe functions, etc) over the actual product itself. This was in our best interest as our product was useless unless recipients could get email delivered to those that wanted it, but it was eye opening.

Do what Basecamp does [0]. They have one price for any size of customer and more importantly do not let any one customer, no matter how big, pay more for Basecamp and turn into a client as you say.

[0] https://www.inc.com/magazine/201606/jason-fried/saying-no-to...