There were two curses that worked against Karna during the Kurukshetra war: one from a Brahmin and another from his own Guru, Parashurama. Karna wanted to learn Brahmastra vidya from Dronacharya, but Dronacharya refused, citing his antecedents. Brahmastra is based on the Gayatri Mantra, so obviously, it can only be taught to someone eligible to have the Gayatri Mantra. Karna was very keen to get Brahmastra, so he went to Parashurama. When asked about his gotra, he lied, saying that he belonged to the Bhargava gotra, meaning he was a Brahmin. Parashurama accepted him as his disciple and started teaching him. During his stay with Parashurama, Karna accidentally killed a cow that belonged to a Brahmin. Even though Karna apologized profusely and tried to reconcile with the Brahmin, the Brahmin still cursed him, saying that the wheel of his chariot would get stuck in the mud in the battlefield.

Some time later, while Parashurama was taking a nap with his head resting on Karna's thigh, an insect, a beetle, bit Karna, causing him to bleed profusely. Despite the pain, Karna didn't chase the beetle away, lest he disturb his Guru's sleep. The flowing blood woke up Parashurama, who noticed the blood and concluded that Karna was not a Brahmin because a Brahmin could never tolerate pain to this extent. Karna admitted that he was a Suta and that he had lied to Parashurama to obtain Brahmastra. Parashurama also cursed him, saying that Brahmastra would never work for him, and sent him away.

Karna faced the consequences of his actions. This underscores that even unintended offenses carry their weight, and any ill-gotten gains, such as knowledge obtained through deceit in this case, are bound to crumble under the weight of their own dishonesty.