Paritrāṇāya sādhūnām, vināśāya cha duṣkṛtām, dharma saṁsthāpanarthāya, sambhavāmi yuge yuge
~ Bhagavad Gita
(In order to deliver the righteous, to destroy the unjust, and to resurrect the principles of religion, I appear millennium after millennium)

The Mahabharata is an epic that contributes immensely to the Indian way of life. There are quite a few lessons one can learn from the various characters of the longest poem that was ever written.
Krishna:
Krishna chose to stand for what was right & was willing to go to war for it. In the time of doubt, the 8th avatar of the Vishnu recited the Bhagavad Gita to Arjuna, preaching to him that one must be unwavering in discharging one’s duties, even in the most challenging times. revealing his cosmic form.
Arjuna:
Arjuna was a warrior with godly skills, but he was too self-centered to be humble. The warrior hero in the epic teaches us to execute an assigned task with utmost concentration. At the same time, one must not be arrogant of one’s skills, for arrogance can often be humbled.
Karna:
Karna is known for his generosity & his loyalty to his friend Duryodhana. Karna could never refuse to help those who asked for it. The first-born son of Kunti is the hero that was bound by honour to chose the wrong side. He teaches us kindness & generosity.
Yudhishthira:
Yudhishthira is known for being the most righteous man of his time. He teaches us that all of us, have weaknesses. Even righteous Yudhishthira fell prey to his weakness of gambling where he lost his kingdom, his brothers, himself & his wife. Greed can cloud one’s judgement.
Dronacharya:
Guru Dronacharya, the master of arms & royal teacher favoured Arjuna in spite of Eklavya being better than him. Later on, he refused to fight under Karna in the Mahabharata, not because of his skills, but his caste. He teaches us that talent is what matters, not one’s status in life.
Draupadi:
Draupadi took excessive pride in her beauty & had insulted Karna & Duryodhana with her acerbic words. The wife of the Pandavas teaches us to not be excessively proud of one’s beauty & not to talk to people in a derisive manner. We must learn to be gentle with our words.
Abhimanyu:
Abhimanyu was one of the handful warriors who knew how to penetrate the Chakravyuh (lotus formation) but did not know how to escape or exit it. He died fighting valiantly. He teaches us that incomplete knowledge can be dangerous.
Dhritarashtra:
The father of the Kauravas was so blinded by his love for his children, he chose not to stop Duryodhana & his brothers from committing blunders that eventually led to their end. We learn that it is important to correct our loved one when they’re wrong.
No matter the good or bad,if you believe in it, FIGHT and WORK for it, to your last just like the Kauravas. Don't get influenced by the obstacles in your life, keep moving on, just like Pandavas.No matter what it is useless to tell truth all the time ... every time, learn from the mistakes Dharmaraju made