It is the ego that causes frictions and differences of opinion. At the slightest provocation a person flares up and there is a breach of discipline. One should exert oneself to have control over the mind. The ego of a person is present even in childhood and one feels insulted if asked to apologize for the abuses hurled at one's sister. I remember, in my childhood when an option of apologizing or eating cow-dung was open to me, I ate cow-dung but did not apologize. On introspection, we notice that it is not the external agency which provokes an individual but the human weaknesses are a cause to it.
There are six adversaries of human being as narrated by our ethics viz. attachment (Kama), anger (Krodha), avarice (Lobha), delusion (Moha), conceit (Mada), and jealousy (Matsara). When a person is under the sway of any one of them, he loses his self-command. One ceases to be in his normal self when he is overpowered by anger. As the Bhagavad Gita states:
Krodhatbhavati sammohaha Sammohat smriti vibhramah
Smritibhrumshat budhdhinasho Budhdhinashat Pranashyati II.63
Thus when vision of Oneness and the mission of life is lost, discrimination is lost and conscience is silenced. The anger in this verse can be replaced by any one of the other five and the train of miseries follows the same way.