In the epic, the Mahabharata, on the final day of the lessons from his guru, Parashurama, Karna bravely bore a scorpion’s sting while Parashurama was resting his head upon his lap. As the blood from Karna’s thigh trickled down and disturbed the sleeping Parashurama, he realized that only a Kshatriya (a warrior) could bear such pain without a murmur and that he had been tricked by Karna into believing he was a Brahmana (of the priestly class). Karna explained that he was actually a Suta (a mixture of Brahmana and Kshatriya) in an attempt to placate his irate teacher. Furious at being deceived, Parashurama cursed Karna that he would be unable to use weapons, especially the Brahmastra, when he needed them the most. This curse came into effect when Karna was unable to remember the incantation to invoke the Brahmastra while fighting against Arjun on the battlefield.