I think it is not so much a of the fear of the unknown , but not wanting to let go of life, life experiences and loved ones. I remember going out on my first hunting trip. I had descented and went to my spot in the middle of the woods before dawn. Sitting in the quiet, listening to the sounds of nature, watching for the buck and watching the sun come up. Never have felt that at peace before or since. My wife and I had gone to Helen Georgia last year for our anniversary. We went to one of the waterfalls there. It was quite a hike getting to it, but it was worth it. These are things that are tangible, that we can experience, touch, smell, taste, see. These are things that we cherish. We don't know what lies beyond, other than what we think, what we are told through religion, spirituality. I would miss all of this, as well as my friends and loved ones. God has created a beautiful planet for us, according to my beliefs. I know that, according to scripture, heaven is peace, tranquility, no fear, no pain, no sorrow. But it is beyond my meager comprehension. We, as humans and mortals, know the here and now. We know what we can see, touch, taste, smell, hear and we are comforted by that "normalcy". It is not so much the fear of the unknown, but the fear of giving up the known. At least, this is my humble opinion.