What role can a disciple play in Guru’s life?

Gurudev, Lord Krishna played the role of a Guru to Arjuna. In Lord Krishna’s life, what role did Arjuna play? What role can a disciple play in Guru’s life?

Sri Sri: There can be only two types of disciples: the easy disciple, and the tough disciple. The tough ones are hard nuts to crack. It will take a long time for the tough ones to get the point.
The easy ones are those who know, who become sensitive, and who get it. You can say, like a buffalo or a cow.
If you just shout ‘Aye!’ to a cow, it understands and moves forward. But for a buffalo, you have to take a big bamboo stick and hit it lightly to really get it to move; only then it will move. Or you have to literally come and push it with your hands.
So these are the two types of disciples. Ones who listens easily and gets it, and who is sensitive, The other doesn’t listen, and takes a long time to get the point.