There will be a limitation for the development of anything.If the limitation is approriately taken control,things will run smoothly.Contrarily,if the limitation is broken through,things will go bad.People's selfishness is just as what the above depicts.It is necessary to control the selfishness to a certain degree to leave room for people's living and improvement.When the selfishness is out of control,it will be like flood,bringing about endless disaster.