The left-hand box

The mistake

Two identical machines sit side by side with no reliable identification — the only labelling was done by hand years ago and has since fallen off, so the operator is working from memory and a colleague's equally unfounded confirmation rather than from any check against the running system. Nobody verifies what the box actually does before power-cycling it: no hostname lookup, no console, no glance at the machine's own status display, which is showing a payroll job in progress. The result is that a restart intended for the shop server is applied to the payroll server mid-run, re-triggering a completed pay cycle, while the shop stays down because it was never touched.