In truth, however, the missing stair is an illusion. You see, the extra stair really does exist, just not strictly in the physical realm. Ordinarily you don’t know it’s there. When the lights are on and you can see where you’re going, your physical senses are in control and you only sense the steps that have a solid physical form. But when it’s dark, or you’re carrying a large object that obscures your view of your feet, or your attention is simply elsewhere, then your subconscious awareness of things that are not purely physical can become engaged. The stair you tried to step on isn’t really missing- it’s just hidden from the physical world.
That heart-wrenching feeling of impending disaster that you feel when you try to step on that extra stair and pass right through it is not a lie. Every stair step leads to somewhere, and this one isn’t an exception. If you were to succeed in stepping on that extra stair, you would step up into a different dimension and cease to exist in this one. Although these dimension doors can exist in many places, they tend to show up in stairways because stairways are by nature liminal spaces- that is, they are transitional, in-between, neither of the floor below nor the one above. The dimension that the extra stair leads to goes by many names- the Ether, the Great Beyond, the Afterlife, the Spirit Realm, Heaven, Hell, Purgatory, the Happy Hunting Grounds- what you call it isn’t significant. The main point is that if you step on this stair, your life on this earth is no more. When your feet are both solidly on the ground again and you feel that you’ve just had a near-death experience, it's because you really have.
Even so, there’s no reason to fear the extra stair. Though our occasional encounters with it may be startling, there is little risk of accidentally stepping out of this world and into the next during a routine trip up the stairs. There is a specific time appointed to each person when passage between the dimensions is permitted. If it isn’t that time, then your foot will simply fail to contact the extra stair, and you will stay in this world.
When your appointed time does come, and you step onto the extra stair and find that it is solid beneath your feet, do not fret. It’s only a small step up to a floor you haven’t yet explored.
This piece is inspired by the following quotation, which I found to be of great help when my Grandma took the final step up.
“It is a curious thing, the death of a loved one. We all know that our time in this world is limited, and that eventually all of us will end up underneath some sheet, never to wake up. And yet it is always a surprise when it happens to someone we know. It is like walking up the stairs to your bedroom in the dark, and thinking there is one more stair than there is. Your foot falls down, through the air, and there is a sickly moment of dark surprise as you try and readjust the way you thought of things.”
-Lemony Snicket, The Reptile Room