Brian Sutton-Smith wrote “The opposite of play isn’t work. It’s depression. To play is to act out and be willful, exultant and committed as if one is assured of one’s prospects.” in The Ambiguity of Play (1997) which I read a while ago and now I found it cited in Unlearning How to Teach, Creativity or Conformity? Building Cultures of Creativity in Higher Education by Erica McWilliam. And a brief further search brought up the image above here.