There is no reason why the entire army of the kings on one side is incapable of conquering the single Dhananjaya. Covered by arrows shot by Bhishma a hundred times.
कस्मादशक्ता निर्जेतुमिति हेतुर्न विद्यते। शरवातैस्तु भीष्मेण शतशो निचितोऽवशः॥