||Why do people walk up stairs, but do not walk up escalators? The rationale for walking up stairs is obvious if you just stand still, you won t get anywhere. If the benefit of getting to the top of the stairs exceeds the cost (the walking effort) you’ll walk up the stairs. So why do most people stand still on escalators? This is a bit of a puzzle because the cost of walking is the same whether you are on a staircase or an escalator, and in both cases, walking allow you to arrive sooner and spend more time at your destination. We can use the marginal principle to solve this puzzle. Suppose you re on the way to listen to a free concert, and you’d be willing to pay $10 to hear the music. Suppose your cost of walking up a long staircase is $3 that s how much you d be willing to pay to avoid the staircase. Walking the staircase generates a net benefit of $7 = $10 – $3, so climbing the stairs is sensible. Suppose that the following week you have the same music opportunity, but there is an escalator instead of a staircase. If you stand still on the escalator, you’ll get the $10 benefit without any walking cost, so your net benefit would be $10. If you walk up the escalator, you will arrive at your destination sooner and get to listen to more music, but there would be a $3 walking cost. Should you walk or stand still? It depends on the marginal benefit of the extra music you will hear if you walk up the escalator instead of standing still, compared to the $3 marginal cost. If arriving sooner generates an extra benefit less than $3, it will be sensible for you to stand still, like most people.