Not knowing his true identity, he was ridiculed throughout his life as a “Soot Putra”(charioteer’s son) while he was actually “Surya Putra” (Son’s Child).
He lost in the battlefield to Arjun because of sage Parshuram’s curse which he got for his “sin” of tolerating pain rather than disturbing his master’s sleep. He was killed unarmed by Arjun who justified his action by saying that his son Abhimanyu was also killed unfairly. But before the killing of Abhimanyu, Bhishma Pitamah was killed by Arjun standing behind Shikhandi using him as a weapon as he knew Bhisma would not lay a finger on a person who was a woman in his previous birth.
So was the killing of unarmed Karna (even without his birthmarks of kavach and kundal which were taken away from him in the form of slyness taking advantage of generosity) justified?
Isn’t it strange that Yudhisthir who didn’t think twice before placing his wife on gamble is known as ‘Dharmaputra’ whereas Karna who did not hesitate to give up his life in charity is deprived of honour?
Coming to Karna's decision - Even after he finds out who he really is- a Pandava, he decides what he wants to be is really something different, something he has made himself in all the years of his training and thinking.
This is the reason that Karna is remembered today and honoured as a true warrior.
This teaches us something – we can be anything we want to be in life, simple accidents of birth need not determine them, we can overcome them.