1. We have the natural instinction to walk up or down a flight of stairs. We take advantage of the natural design of stairs, so sometimes when we fall down, it’s the designer’s fault not our clumsiness. There are cases where we are used to the standardized measurement of a flight of stairs, but when the design is altered, we can fall.

http://www.youtube.com/watch?v=kWo2WdJgWIE