Once Arjuna asks Krishna why Yudhishthira is called Dharmaraja (Religion king) and Karna as Daanveer (Donation king), as both never refused alms to anyone. Krishna says, wait for some time &I will let you know.
After a month, in whole kingdom it was raining heavily, both (Krishna and Arjuna) in disguise of Brahmins (wise men/priests) first go to Yudhishthira, saying that we are doing a Yagna and need 100Kg of Sandal wood. Yudhishthira immediately sent his servants across the kingdom, and later regretfully refused by saying that it is difficult to find dry Sandal wood anywhere as its raining heavily. Let me know if I can arrange anything else for you. Both Brahmins said “thanks” and left the place.
Then they went to Karna and made the same demand. Karna thought for a while and said it is raining heavily outside, it is least likely to get dry Sandal wood. He takes out his bow and arrow and cuts all windows and doors of his palace and compiles them for the Brahmins.
Later Krishna says to Arjuna, it is not that Yudhishthira would have refused if we would have asked for wood from his doors and windows. But this idea didn’t strike Yudhishthira in first place. Yudhishthira donates because it is written in Dharma (religion), Karna donates because he likes to do it.
The message of the story is very subtle. So many times in our personal and professional life we are doing just for the sake of doing it. There is no heart and soul into it. There is no passion for doing it.