"Vanity, when it passes beyond a point, kills pleasure in every activity for its own sake, and thus leads inevitably to listlessness and boredom. Often its source is diffidence, and its cure lies in the growth of self-respect. But this is only to be gained by successful activity inspired by objective interests."
January 1, 1970
https://en.wikiquote.org/wiki/The_Conquest_of_Happiness