It's all about the Johann Hari Ted talk, pointed to by Clod here (I hope this is the one I'm thinking of):
https://cellar.org/showpost.php?p=1010965&postcount=5
Give rats in standard lab cages morphine, and they take right to it. But put the rats in a beautiful "
rat park", with other rats to be social with, and lots of space to explore, and wheels and things; and they reject the morphine.
Without meaning, without fulfilment, we are just rats in a cage.