It isn't a matter of trust, its a matter of developers are humans. Humans make mistakes, and continuous integration helps catch mistakes.

I've been coding for 25+ years, and I sometimes I forget to remove debug output, or I forget to update an explicit exception I threw somewhere, or I forget to make sure dependencies build across all the platforms we need.

Running your build a second machine helps to catch a lot of those mistakes. It also helps enforce automation and good configuration practices and lint/formatting standards and all that, but fundamentally its helps us because humans make mistakes.

CI doesn't have to mean setting up a 12 step pipeline in GH actions with 3k lines of yaml and crazy triggers and workflows. It can just be an old dev machine (https://www.jamesshore.com/v2/blog/2006/continuous-integrati...) that pulls the latest code, runs `script/build`, and POSTs results somewhere.

Maybe local signoff works for 37signals, if so, thats great. But it isn't continuous integration.