We are sure that the shadows exist because we can see them. Existence concerns what can be defined, yet the only thing definable in case of a shadow is what creates it: light and a barrier.
Shadow is where the light does not exist. To talk about a shadow, we point out to the barrier that obstructs the light. The Shadow leads us to the barrier. It is our anticipation of the barrier obstructing the light that helps us recognize this undefinable thing — an undefinable thing that has the power of refreshing us in hot summer days.

It seems paradoxical that something undefinable can produce tangible feelings. Shadow persists in existing through our definitions.
As a matter of experience, for every material object, there corresponds the possibility of its shadow; but when we turn off the light, Shadow ceases to exist. So relying on our senses, its existence is not monumental but ephemeral.
Rather than a solid material, Shadow is a contradictory possibility. It is an elusive being between a déjà vu or a prediction.
Shadow resembles the possibilities like hope and despair. For every material object (or every event with material consequences), there corresponds the possibility of hope and despair. Hope indicates a barrier that gives rise to it. In a city destroyed in war, or in a living creature in a mortal condition, hope and despair coexist. Despair is the endless doubt that the shadow is merely an illusion.