A dog will pursue rabbits to the point of complete exhaustion and be happy all the time, but if you put the dog on a treadmill and gave him a good dinner after half an hour, he would not be happy till he got the dinner, because he would not have been engaged in a natural activity meanwhile. One of the difficulties of our time is that, in a complex modern society, few of the things that have to be done have the naturalness of hunting. The consequence is that most people, in a technically advanced community, have to find their happiness outside the work by which they make their living. And if their work is exhausting their pleasures will tend to be passive.
Source: Bertrand Russell : The road to happiness (1952)
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