The more fearlessness evolves, that much more available and vulnerable you become. That is why sadness and gentleness are part of fearlessness. The joy of fearlessness brings the sadness. Real fearlessness is like mixing sweet and sour together. The tone of joyful sadness is like the sound of a flute, which is so melodic and beautiful. It ravishes your mind. It is not accompanied by any other musical instruments. The solo melody of the flute brings the echo of emptiness into your mind.
From Smile at Fear: Awakening the True Heart of Bravery, by Chögyam Trungpa, page 78.