Los cuarenta y cinco minutos de Knight Capital

There is not a single stupid decision in this story if you look at each one separately. The new code, by all accounts, was written correctly. Reusing a free switch is ordinary practice. The technician made the kind of mistake all people make. The disaster arose at the joints: between the change of 2005 and the code nobody checked after it, between the new code and the old code someone forgot to delete, between the switch and its previous meaning, between eight servers that were supposed to be identical. Each link looked sound on its own, and together they brought the company down.