“If you’re sitting there watching the system and it’s doing great, it’s very tiring.” In fact, it’s extremely difficult for humans to accurately monitor a repetitive process for long periods of time. This so-called “vigilance decrement” was first identified and measured in 1948 by psychologist Robert Mackworth, who asked British radar operators to spend two hours watching for errors in the sweep of a rigged analog clock. Mackworth found that the radar operators’ accuracy plummeted after 30 minutes; more recent versions of the experiment have documented similar vigilance decrements after just 15 minutes.”
This is somehow related to this - about how an audience might pay attention.