I used to ride my bicycle around the top of a large hill.  It went up and down, but I ended up in the same place that I started.  One would think that, since I ended up in the same place, I necessarily went up-hill and down-hill the same amount - but not true!

It took me an hour to ride around that hill.  The up-hill parts were hard and I went slowly.  The down-hill parts were fast and easy.  Turns out, I'd spend 45 minutes going up-hill and 15 minutes going-down-hill.  Not equal!  So, while I may have "theoretically" went up and down the same amount.  In terms of time and my perceptions, it was up-hill most of the way!

Blake McBride