Karna was rightly called Dhaanveer. Prabhu Krishna offered the throne of Hastinapur. He rejects and says I will be loyal to my friend Duryodhana. Only a great man can do.
Shakuni sent Duryodhana to Sahadeva to ask the muhurat (right time) of the Mahabharat War. Sahadeva being honest had disclosed it to Duryodhan in spite knowing the fact that Duryodhan was his real enemy in the battle.
Sahadeva could already see the great war coming however he could not warn his brothers because he had a curse - The moment he would reveal the future he would die and so Lord Krishna had advised him to answer questions wrt to future only in the form of questions.
