One habit I have to break is treating the operating system as a black box. 25 years of Windows development has done this to me. Under Windows, I can’t sneak into the operating system source code to see what’s going on underneath the hood, so I don’t try to do so. With OpenBSD, of course, all the source code is published, so I could go there—but I don’t. This is silly; it’d be much easier to solve a problem if I checked how the operating system actually behaved, rather than depending on the (excellent) documentation. The documentation isn’t wrong, incidentally, it just doesn’t go to the detail of the source code.