rivalry among siblings

many don't believe that there always been rivalry or frictions among siblings or sister company or subsidiaries.
one of my friend called it undercurrent.

why this rivalry or frictions happened?
why cant blood brothers or sisters resolve amicably any dispute between them?
who really can manage all this rivalrly or frictions?

some seen it happened but thought its small matter only. but over years it become very ugly. not only they cannot working together but also hate each other.

until now i still dont understand why it happened.
it is because of money? i dont really think so
it is jealousy?
it is purposely create to get attention from father or head of group? this one maybe..........

can this undercurrent been manage by ordinary manager or head of company or other big brother?

next two years, i may have the answer.......hopefully