*Life's unfairness does not give you license to walk the wrong path of dharma!*
Karna asked Krishna - "My mother left me the moment I was born. Is it my fault I was born an illegitimate child? I did not get education from Dhronacharya because I was considered a non Kshatriya. Parshuram taught me but then gave me the curse to forget everything since I was a Kshatriya. A cow was accidentally hit by my arrow & its owner cursed me for no fault of mine. I was disgraced in Draupadi's swayamvar. Even Kunti finally told me the truth only to save her other sons. Whatever I received was through Dhuryodhana's charity. So how am I wrong in taking his side?"
Krishna replies, "Karna, I was born in a jail. Death was waiting for me even before my birth. The night I was born I was separated from my birth parents. From childhood you grew up hearing the noise of swords, chariots, horses, bow and arrows. I got only cow herd's shed, dung, and multiple attempts on my life even before I could walk! No army, no education. I could hear people saying I am the reason for all their problems. When all of you were being appreciated for your valour by your teachers I had not even received any education. I joined gurukula of Rishi Sandipani only at the age of 16! You are married to a girl of your choice. I didn't get the girl I loved & rather ended up marrying those who wanted me or the ones I rescued from demons. I had to move my whole community from the banks of Yamuna to a place far off the seashore in order to save them from Jarasandh. I was called a coward for running away. If Dhuryodhana wins the war you will get lot of credit. What do I get if Dharmaraja wins the war? Only the blame for the war and all related problems.
Remember one thing Karna. Everybody has challenges in life. LIFE IS NOT FAIR ON ANYBODY. Dhuryodhan also has a lot of unfairness in life and so has Yudhhishthir. But what is Right (Dharma) is known to your mind (conscience). No matter how much unfairness we got, how many times we were disgraced, how many times we were denied what was due to us, what is important is how you REACTED at that time. Stop whining Karna. Life's unfairness does not give you license to walk the wrong path of dharma!"