I was part of an electrician team renovating a three-letter agency's main data center (adding UPS to an archaic government renovation). As part of this process, we had to isolate the Emergency Power Off system/buttons.

Unfortunately, the EPO ended up having been installed differently than the plans indicated [0] — there was definitely more than an hour of unexpected downtime figuring out how to "unrig" its decades of faithful misconfiguration.

During this same months-long modernization, a separate facility decided to install a temporary tap off our already-temporary taps (no engineering consultation attempted) — with resulting Megawatts of melting disaster. More hours downtime.

tl;dr: shit happens

[0] EPO's main neutral was tied into a general lighting circuit's j-box, some bullshit jerryrigging from an 80s sparkie; our apprentice was tasked with taking out old fluorescents... ended up taking out entire facility (through no fault of his own).