Or the electrician doing maintenance on the backup generator doesn't properly connect the bypass and no one notices until he disconnects the generator and the entire DC instantly goes quiet.
Or your DC provisions rack space without knowing which servers are redundant with which other servers, and suddenly when two services go from 10% CPU use to 100% CPU across ten servers the breaker for that circuit gives up entirely and takes down your entire business.
Or the electrician doing maintenance on the backup generator doesn't properly connect the bypass and no one notices until he disconnects the generator and the entire DC instantly goes quiet.
Or your DC provisions rack space without knowing which servers are redundant with which other servers, and suddenly when two services go from 10% CPU use to 100% CPU across ten servers the breaker for that circuit gives up entirely and takes down your entire business.