The Curse of Parshuram on Karna: Deceit and Consequences in the Mahabharata

Parshuram had taken a vow of not teaching to the Kshatriyas. He was never against Kshtriyas as a caste, but due to their Adharmic path, such as not fulfilling responsibilities of Kshtriya Dharm, being busy in enjoyments, drinks, and women, he killed all Adharmic Kshtriyas and took a vow of not providing any education to them.

Parshuram taught Bhishma even though he was a Kshtriya. This was because Bhishma was not a tyrant and was following his moral Dharma. And moreover, Parshuram was a Rishi and the incarnation of God, he could easily see that Bhishma was not an ordinary man, thus Parshuram liked him, broke his vow and accepted him as his pupil and taught him.

Karna disguised as branhim acquired siksha from Parashuram, which led to a great annoyment for Parashuram:

Karna was keen to acquire the Brahmastra mantra from the great teacher Parshuram. However, he knew that Parshuram gave instructions to Brahmins (the priestly tribe) only. So he disguised as a Brahmin and beseeched Parshuram to accept him as a shishya(disciple). Parshuram accepted him as such and started giving him instructions. One day when Parshuram was resting in Karnas lap, it so happened that a bee stung Karna on the lower portion of his thigh. It was very painful and he started bleeding. However, fearing that if he moved his legs, he would awaken Parshuram, he did not move at all and continued to suffer. When Parshuram woke up, he saw Karna bleeding. He asked, Son, tell me truthfully who you are? A Brahmin cannot suffer so much physical pain. Only a kshattriya (the warrior tribe) can endure so much discomfort. Karna was obliged to disclose his identity. Parshuram was greatly annoyed because he was a sworn enemy of Kshattriyas. He therefore cursed Karna that as he had learnt through deceit, he shall forget the vidya (skill) which Parshuram had taught him at the crucial juncture.