Dronacharya had to lie on the bed of Thorns.

During Mahabharat war Dronacharya was falsely informed that his son Aswattthama hadbeen killed.Hearing this news Dronacharya's heart was badly shattered and he lay down on the bed of thorns after he was killed by the son of Drupad.But he was waiting to breath his last when northern movement of the sun comes.Thus he was waiting for Makar Sankranti.When Lord Krishna was asked the reason for lying on the bed of thorns he said that in previous birth Dronacharya had thrown a snake on thorns so he was compelled to lie on the bed of thorns in this life.Newton had rightly said"Every action has equal and opposite reaction ".