Why do the hands on clocks go "clockwise?" Seems like a circular definition, but if you looked closely at sundials in the northern hemisphere, you'd notice that the shadow of the sun moves around the sundial in a "clockwise" direction. This was adopted by clock-makers and became the standard we know today.

In the southern hemisphere, the sun's shadow moves around the dial in the opposite direction, so if clocks had been invented there, our watches would move the other way.