Dual forces

A very simple analogy between circle (its circular motion) and our regular life :
Both exist due to dual forces...

Physics says that an object is in circular motion due to dual forces named Centripetal (one which pulls it inward towards the center) and Centrifugal (one which pulls it out, along the track).

Thinkers round the world never get tired of talking about dual forces of life. The couple's name change but they always appear as twins: Shiv and Shakti, Yin and Yang, Day and Night, Good and Bad, God and Satan, Happiness and Sorrow...

Somehow one can't exist without the other. :)