> maintaining a Great Circle Route other than the equator was effectively impossible until the 1800s. It was at sea because the sea is constantly forcing your

> maintaining a Great Circle Route other than the equator was effectively impossible until the 1800s. It was at sea because the sea is constantly forcing your ship to change heading (wind, currents, etc.), and you have to compensate for that, and before the required navigation techniques were developed, there was no way to know what heading you should be on at any given time to maintain a great circle route. But the article is asking you to imagine that you don't have to worry about that--which, if you're just walking across flat land, you don't. You can just "put one foot in front of the other", doing what comes naturally, and you will follow a great circle--not a curve of constant latitude.