(Oppostion of man in physical nature) How to get across a river?
possible resolutions: swim, ride a boat or canoe...
*Build a bridge (Taking the extremes of the potential response and envelope them in the design).
Without a bridge things would take longer to do. For example, let's say you were hungry and there's some food on the other side of the river but in order to eat, you have to build something or swim to get across. So much energy is saved if all you have to do is walk across a built structure that could last very long.