Stray birds of summer come to my window to sing and fly away。 And yellow leaves of autumn， which have no songs， flutter and fall there with a sigh。

Flow is being completely involved in an activity for its own sake. The ego falls away. Time flies. Every action, movement, and thought follows inevitably from the previous one, like playing jazz. Your whole being is involved, and you're using your skills to the utmost.

Stray birds of summer come to my window to sing and fly away. And yellow leaves of autumn, which have no songs,flutter and fall there with a sigh.