Dhritarashtra is like a pond whose waters are warm on the surface in summer, but whose waters are in fact cold as when one gets in deeper. Dhritarashtra appears to nurture warm feelings towards the Pandavas, but in fact is jealous of the Pandavas.
Bhishma says that just as Dhritarashtra thinks he is entitled to the kingdom, so do the Pandavas think of the kingdom as theirs. As for Bhishma himself, he cannot discriminate between the sons of Dhritarashtra and the sons of Pandu. So he suggests that half the kingdom be given to Duryodhana and the other half to Yudhisthira. Dhritarashtra then seeks the advice of Drona, who says that Arjuna cannot be defeated in war. Vidura says that the Pandavas can never be defeated because Lord Krishna is on their side.
Karna’s advice is the opposite of that given by Drona and Bhishma. He tells Dhritarashtra the story of a lazy king called Ambuvicha, who never paid attention to matters of state. Ambuvicha’s minister Mahakarni then took charge of everything, but was still unable to become the king. So whether one continues to be in power or not is a matter of destiny, and there was no need for Dhritarashtra to have reservations about fighting the Pandavas.
Thus, we find Dhritarashtra, Duryodhana and Karna, all motivated by jealousy. Vidura, Bhishma and Drona offer valuable advice to jealous Dhritarashtra, which he ignores.