It works because he is targeting a subset of all users. He is willing to give up on some potential customers who want some features that the product does not of

It works because he is targeting a subset of all users. He is willing to give up on some potential customers who want some features that the product does not offer. He is also willing to lose actual customers who outgrow the product to competition. I think it works because he hasn't yet reached the critical mass of users when it doesn't. It is probably a good strategy ("do things that don't scale"). GitHub did the same thing, by the way. Remember slide 56 of this slide deck from 2011: https://speakerdeck.com/holman/how-github-uses-github-to-build-github https://speakerdeck.com/holman/how-github-uses-github-to-bui...? Since then a lot happened, including https://github.com/dear-github/dear-github https://github.com/dear-github/dear-github. Regarding another of Joel's products, this was the top comment on the HN thread "Why Fogbugz lost to Jira": https://news.ycombinator.com/item?id=10314403 https://news.ycombinator.com/item?id=10314403