It is important to understand the reasonable possibility of immediate happening of the most dreaded in our life. We live our life with eyes closed and mind shut to the thoughts which are fearsome to us. And this we do despite the reasonable likelihood of their imminent occurrence. Why do we do that? To continue with our easy cozy life so that our comfort zone is not disturbed!
A thinking man, once he understands it, starts looking at this whole phenomenon of fear. He realizes that fear is a natural resultant of the helplessness one perceives of oneself. There would be no fear, obviously, if we are capable of altering the apprehended course of action. But, it is common knowledge that we are helpless! Helpless on so many fronts! In fact, utterly helpless! Still, we believe that we can really plan our affairs and that we and our life constitute some significant phenomenon in this infinite universe.
A view of earth from the window seat of aircraft helps. A view of starry sky helps. Study of astrophysics helps. It helps to take a proper view of our life in this infinite stretch of space and time. It spells our insignificance to us. It may lead us to a feeling of nothingness, of vacuum.
However, at this juncture, comes the emphatic and apparently unimaginable and irrational statement from Shruti. It states that you are infinite. That what you regard as real is unreal. That you alone are source of everything, of even space. That the entity which regards itself as sad, helpless and frightened is unreal and non-existent. It propels us to find out that entity which feels itself as constrained, limited and bound. It states that once you do that, you will find your true Self. You will then understand your own true Self. And then you fear,then you dread, if you can!