The considered wisdom in positive psychology is that to feel better, you just need to think happy thoughts. If this conjures up the song “I Whistle a Happy Tune,” then you’re on the right track.

September 13 is now celebrated as Positive Thinking Day in several parts of the world. It was first observed in the US in 2003 and has since become an annual reminder of the strength positivity holds.

People often attribute the source of their anxious suffering to external situations, such as “meetings make me feel trapped and anxious” or “highways give me panic attacks” or “I can’t stand being ...