In history: in battles during war

In Government:politic parties fighting over different political topics then coming to an agreement. 

In economics: rival companies such as Coco Cola and Pepsi

related to sociology: when people interact with people that they think are different

related to psychology: fighting on sides for something then finally agreeing with the other side because you don't want to look like a fool.

In your everyday life:when you are shopping for something and you will either continue to look for something till it is cheaper somewhere else or you will just buy it the first place you see it.