If that guy has any way of making a mistake, he will.
—Capt. Edward A. Murphy (1949)
If it can happen, it will happen.
—George Nichols, present when Murphy blamed his technician for a failed test.
Industrial processes need feedback controls to handle things that happen. A process that is set up and running is subject to disturbances. Some processes will recover by themselves but others need help. The speed of a steam engine is an example, as it could increase until the engine flew apart if the speed was not fed back to the steam supply valve.
Processes involving chemical reactions work best when materials are added and withdrawn according to the conditions of the equation for the reaction. This requires ...