imagine hitching a donkey and an elephant to a wagon. they both want to go north. so they're pretty happy pulling the cart generally north. but really the donkey wants to go a little bit west of north. so the donkey starts pulling a bit west. but the elephant wants to go a bit east of north. so he starts pulling harder to the east. which make the donkey turn more west. which makes the elephant turn more to the east. and so on. until eventually the the donkey's headed due west. and the elephant's headed due east. and now neither are happy. cause the wagon's not goin nowhere. sometimes the elephant is stronger and pulls the cart east. sometimes the donkey wins. it's a pretty messed up system.