I don't know what fun is, honestly. And I don't really think there is a substantial scientific research literature that's indexed under fun. The word originally comes from the word for hoax or dupe. But apparently it was an invention of the French,. They said that France basically invented the concept of fun in life along with jousting and lace.
Why does time fly when you’re having fun? How do you teach rats to play hide and seek? And what does all this have to do with Anne Boleyn?