After the industrial revolution, we started to use giant machines containing huge amounts of energy. Regardless of the form of energy, its dangerous for us. So we had to isolate all of that energy in the machine. In late 80s US Government enacted a law called “The control of hazardous energy (lockout/tagout)”. This law obliges industrial personnel to lock and tag all energy control points during a maintenance or repair activity with a tag containing your full name and departmeent.