Each link in the chain is itself manufactured/created/constructed. If the weld is bad, the link may fail. "every grain boundary" is not formed in the same way

Each link in the chain is itself manufactured/created/constructed. If the weld is bad, the link may fail. "every grain boundary" is not formed in the same way each link is. The analogy is solid - actually, it's very good in that it conveys clearly and succinctly the concept the parent was asking about without introducing extraneous concepts. Very much in the flavour of EWD: "The purpose of abstraction is not to be vague, but to create a new semantic level in which one can be absolutely precise."