The belief that it is unlucky to pass anyone on the stairs going in the opposite direction, has a biblical foundation. It goes back to Jacob’s dream of the ladder (related in the Book of Genesis, Chapter 28), on which he saw angels ascending and descending.
No one ever knows whether the apparent human passing on a stairway is not in reality a divine being ‘going up’ or ‘coming down’. In any way to obstruct messenger from God would be disrespectful. One’s presence on the stairs might make him change direction and causing to delay his progress. To avoid any such possibility with its awful consequences, it was best never to pass anyone on the stairs.