Newton's Third Law of Motion. Instead of posting links and quotes just google the title, it will be worth it to see other perspectives and how it effects nature. I am primarily interested in examples that may go beyond motion and how it is true for other forces or objects. Does everything have an equal and opposite? We can look at the obvious male\female, good\bad, happiness\sadness, day\night etc. Posted in General Philosophy so as not to discuss the "Law of Motion" itself but to see how it is evident in other things. Where is this not true in other aspects of life?