Mahabharata covers the years following the Pandavas' arrival in Hastinapura in rich and inviting detail - the growing rivalry between Duryodhana with his 99 brothers, on the one side, and the five Pandavas, with their supporters, on the other; Duryodhana’s attempt to assassinate the Pandavas by burning the house in which they are visiting; their escape and their subsequent period of exile. For the purposes of plot advancement, the two most significant events of that period were the arrival on the scene of Draupadi, who became wife to the Pandavas, and Krishna, who became their most trusted friend, counselor, and ally.
Arjuna actually won Draupadi’s hand at her svayambara, the Maiden’s Choice festival at which suitors contend for the love of the princess. Arjuna was the only one in the arena who could string and fire the massive bow that Draupadi’s father had made to test his daughter’s suitors. The family was living in exile at the time, disguised as brahmanas, student priests, and begging for their food. When Arjuna arrived with Draupadi at the door of the hut in which they were living, he jokingly called out to his mother, "Come see what I got in my begging bowl today." And Kunti, without looking up, gave a mother’s typical response: "Whatever it is, be sure to share it with your brothers."
A mother’s word is law.
So Draupadi married all five brothers.
Krishna had also been at Draupadi’s svayambara, up from his city of Maratha, and he had watched with keen interest as the stranger dressed as a brahmana had leaped into the arena and bested the finest warrior kings. Krishna was Kunti’s cousin. He knew of the Pandavas’ exile, and he thought he knew who the unknown warrior priest might be. Shortly after the festival Krishna found his way to the potter’s shed where the Pandavas were living with Kunti. He greeted his cousin Kunti, and clapped Arjuna on the shoulder.
"I knew that you were Arjuna."
"And you must be Krishna. We have never met, yet I feel that I have known you."
"Perhaps," said Krishna, "we have been friends in other lives."
"We will be friends in this life," said Arjuna.
"Yes," said Krishna, and they embraced.