A robot was programmed to believe that it liked herring sandwiches. This was actually the most difficult part of the whole experiment. Once the robot had been programmed to believe that it liked herring sandwiches, a herring sandwich was placed in front of it. Whereupon the robot thought to itself, 'Ah! A herring sandwich! I like herring sandwiches.'

It would then bend over and scoop up the herring sandwich in its herring sandwich scoop, and then straighten up again. Unfortunately for the robot, it was fashioned in such a way that the action of straightening up caused the herring sandwich to slip straight back off its herring sandwich scoop and fall on to the floor in front of the robot. Whereupon the robot thought to itself, 'Ah! A herring sandwich ...' etc., and repeated the same action over and over and over again. The only thing that prevented the herring sandwich from getting bored with the whole damn business and crawling off in search of other ways of passing the time was that the herring sandwich, being just a bit of dead fish between a couple of slices of bread, was marginally less alert to what was going on than was the robot.

The scientists at the Institute thus discovered the driving force behind all change, development and innovation in life, which was this: herring sandwiches. They published a paper to this effect, which was widely criticised as being extremely stupid. They checked their figures and realised that what they had actually discovered was 'boredom', or rather, the practical function of boredom. In a fever of excitement they then went on to discover other emotions, like 'irritability', 'depression', 'reluctance', 'ickiness' and so on. The next big breakthrough came when they stopped using herring sandwiches, whereupon a whole welter of new emotions became suddenly available to them for study, such as 'relief', 'joy', 'friskiness', 'appetite', 'satisfaction', and most important of all, the desire for 'happiness'.

– Douglas Adams, Mostly Harmless