If one goes up the stairs one leg at a time, as opposed to using both legs to propel oneself upwards, one has the opportunity in between steps to reflect on one's higher situation almost as if a passenger might notice a change of perspective from a roller-coaster during ascent. If one goes upwards two legs at a time, there is no pause in between step so there is little time to truly experience one's progress. The move upwards with two legs is a seamless move. With one leg, a segmented, disjointed journey, thus allowing the time to experience the experience of one legged ascent. The next time you go up some stairs, try doing it with only one leg. There is a zen hidden within it. Maybe not enough to write a book called "The Zen of going upstairs with one leg" but try it and then try telepathically communicating your thanks to me. I will hear you if I'm on the stairs.