Build-in-public writing is usually described as a transparency practice, and that framing hides the real difficulty. You want the benefits of publishing: distribution before launch, early feedback, and a following that trusts you. You do not want the costs: a competitor reading your next move, a customer holding you to a date, or a comment section doing arithmetic on numbers you never meant to publish.
The useful way to hold both sides is to treat building in public as a spectrum rather than a switch. Founders who take this path still draw boundaries around what stays private, especially revenue numbers and details of failure, as Mercury's overview of the approach puts it. The decision is not "public or not," it is which slice of your work is public.
There is also a sharper risk than embarrassment. Arvid Kahl, who has both practiced and written about radical transparency, argues that agentic coding tools changed the calculus: anyone can turn publicly shared architecture, revenue numbers and feature details into a working competitor in days, and the old safety threshold of $20-30K MRR has collapsed to zero, as he describes in his essay on the increasing risk of building in public. Whether or not you accept that forecast, it points at the same design problem: what a post can say should be chosen before you sit down to write it, not edited afterward.
The filter Kahl proposes is worth memorizing because it is one question: is this interesting to follow, or easy to clone? A post about how you decided something is interesting to follow. A post that lists the exact thing you will build next is easy to clone.



