If he were to fight fairly, Bhimasena will never succeed in gaining victory. If, however, he fights unfairly, he will surely be able to kill Duryodhana.
भीमसेनस्तु धर्मेण युद्ध्यमानो न जेष्यति। अन्यायेन तु युध्यन् वै हन्यादेव सुयोधनम्॥