A weld joint doesn't fail at the center of the bead — it fails at the heat-affected zone, the transition where two different material states meet. The most dangerous place in any system is rarely the obvious stress point. It's the boundary. The 18th-century Scottish philosopher David Hume noticed something structurally identical in how the mind works: our reasoning doesn't collapse at the hard problems we're actively wrestling with, but at the unexamined assumptions we carry across without inspection — the invisible transition zones between what we know and what we merely inherited. On a job site running process piping or power construction, this shows up constantly: the veteran who's run a thousand flanged connections knows the bolt-up cold, but the failure comes at the handoff — the assumption that the upstream crew spec'd the gasket correctly, or that the isometric reflects the as-built. The boundary between your knowledge and someone else's is where the heat-affected zone lives. Treat every interface — procedural, material, human — with the same skepticism you'd bring to an unfamiliar base metal.

What assumption are you currently carrying across a team or project boundary that you have never personally verified?

Drawing from Scottish Empiricism combined with Reliability Engineering — David Hume (An Enquiry Concerning Human Understanding, 1748)