Enjoyment appears at the boundary between boredom and anxiety, when the challenges are just balanced with the person’s capacity to act.

Mihaly Csikszentmihalyi Flow: The Psychology of Happiness

Mihaly Csikszentmihalyi Flow: The Psychology of Optimal Experience (Harper Perennial Modern Classics)

Cal Newport Deep Work: Rules for Focused Success in a Distracted World

LessWrong How to Be Happy - LessWrong

Daniel Levitin The Organized Mind