He wonders: why does light never expose the heart? And he is not talking about medical x-rays. The man in the shadows; you might see him when you look in the mirror. He would rather stay in the shadows and see what light shines on.
People who bask in the light seem bold to be exposed--but they mostly wear masks. The face is unseen and to them, it's all that matters--they can tolerate light as long as the face is hidden. Thus, the man in the shadows sees that light only exposes the physical, not the heart, even if people bask in it. In fact, he sees that shadows can expose more than what light can--shadows exposes the heart.
Soon, the man in the shadows learns that those who abide in the shadows have pure hearts. And those who love staying in the limelight--under the glare of spotlights--only want publicity and showmanship. Wanting to be in the light exposed their hearts, too. They love the applause and recognition and admiration.
Exhaustion brought by the madness of the light makes you a man of the shadows. There you begin to learn life and appreciate the light in the shadows. Light is brighter in the shadows than in excessive and artificial glare. You become like Dracula, but a good one. You understand that survival depends on how well you see in the shadows with little or no light. If you can find your way easily in the shadows, you have no problem traveling in full brightness of light.