In Vyasa's lap as the infant cried and shook his limbs, his right foot hit the sage's chest, and the impact was so hard that he fell down unconscious. When he regained consciousness, he cursed the infant that that same foot be crushed in the battle. It was a terrible curse; as a consequence Duryodhana had to die a slow and painful death, which again was only part his suffering. Apart from the great Bhisma, perhaps no major warrior who fought in the Mahabharata war had to wait for death. But Bhisma's case was different; he chose the time of his death. Given the sage's curse, Bhima was the instrument of destiny when he roared in the Kaurava court before they departed to the forests for their twelve-year vanavaasa and one-year agnyaata vaasa that he would smash Duryodhana's thighs. When he did it in the decisive battle with Duryodhana, Vyasa's curse materialized; he was merely the means.
And incidentally, when Bhima dealt the fatal blow to Duryodhana, he did it not with his mace, but with Krishna's (Vishnu's), kaumodaki, in Sarala's language. He was completely unaware of this fact, as was everyone else, apart from Krishna of course, at whose wish the mace had come to Bhima's hands. No one was privileged to know of it even later. However, this fact is not directly related to Duryodhana's destiny. Its significance lies elsewhere, and we do not wish to dwell on it here.
It was Vyasa's curse that linked Duryodhana with Bhima; nothing in their past existences connected them - very unlike Dussasana and Draupadi, who were linked from an earlier existence. That link ended with the propitiation of the latter in the form of Dussasana's blood on her lips.
Duryodhana of course was born because of a curse, and Vyasa knew it. Duryodhana was no other than Pannanga Narayana himself, who was cursed by Sudraka Brahma to be born in the world of the mortals. The latter had performed most rigorous tapas to please the former, who not only did not respond to his tapas, but also destroyed it with the help of feminine attraction. When Sudraka Brahma realized what had happened, he cursed him. Pannanga Narayana appeared before the great god and pacified him. Sudraka Brahma assured him that he would enjoy a great life in the mortal world, that his divine spouse would join him as his wife, and that his status would be so high that he would not bow down to anyone, human or god. Anyone who dared to receive his bowing would be reduced to ashes. Saaralaa Mahaabhaarata constructs a belief system where an inferior could not receive reverence from a superior in the form of bowing or prostrating at the feet, etc. without being burnt to ashes.
This last assurance was obviously intended to be a boon, but it turned out to be nothing less than a curse. Duryodhana did not bow to anyone, but it would be unsatisfactory to say that it was entirely due to his arrogance, since it could not be due to it that he did not bow to his parents. However, it is not clear whether he had the memory of the boon, that is, whether his not bowing was actually an act of concern and considerateness, or whether that lost memory had taken the form of an almost instinctive action. However if the constraint on him with respect to showing respect was widely known, his own teacher and benefactor Balaram did certainly not know of it. As he was engaged in that decisive fight with Bhima, an angry Balaram appeared, with the intention of intervening in his favour, but withdrew, when on his arrival on the battlefield the Krishna and Pandavas repeatedly prostrated before him, but Duryodhana did not bow down to him. He blessed the Pandavas, chided Duryodhana and left. Human or god, it is impossible indeed to live in the world and not pay for transgressing the moral code of the world. The only one who was unaffected by all this was Krishna.
We need to note that whereas Sudraka Brahma's curse caused the birth of Duryodhana in the mortal world, it was certainly not the cause of his agonizing death in the Mahabharata war. Now a reasonable question to ask is whether Vyasa himself was destiny's instrument. He was not; there is no evidence in Sarala's text to support this.
In any case, destiny worked very differently for Bhima. Soon after his birth, a finger of his left foot hit a peak of the Mountain Satasringa, and it crumbled to pieces. An angry and wounded Satasringa cursed Bhima that he would lose the first time in a battle. Kunti was very upset, and told the mountain that he was grossly unfair in cursing her innocent infant, and cursed him that he would suffer the agony of people cutting away parts of it. The chastised mountain prayed for her forgiveness, and assured her that after his first defeat, Bhima should invoke him, upon which he would acquire such immense energy that he would be invincible in battle.
Sarala's Kunti was a remarkably self confident person. She immediately protested against a very unjust curse, and as a victim of the abuse of power, even went to the extent of cursing the mountain in response, which readily brought about corrective action. In contrast, Dhritarashtra did not utter a word. In so much in awe he was of the celebrated sage, who was also the revered family elder, that it did not seem to have even occurred to him that his eldest child had been unjustly treated. He might also have been too stunned to react to what had happened. Bidura had already suggested that the infant be put to death for the survival of the clan, and a deeply troubled father was seeking Vyasa's blessings in order to negate the impact of the malignant forces that possessed his son. And here was the redeemer who uttered such a horrible curse. Then all said, Dhritarashtra of Sarala was not the man who was capable of protesting, but more about him elsewhere.
Consider Vyasa's conduct. Consider the way he was situated with respect to the children of Gandhari. He was a great sage, learned in the shastras, and he was the knower of the past, the present and the future. He was reverentially called, in Sarala's words, duti krushna ("Second Krishna"). That apart, he was the family's venerable eldest, and as such the protector of the family, which must have primarily been why Dhritarashtra sought his blessings for Duryodhana. Then it was because of his intervention that Gandhari's children were born; thus there was a special bond between them and him, on account of which it would not be unreasonable for Dhritarashtra if he expected that the great sage would protect them.
Surely it did not occur to Vyasa that if the impact of an infant's foot was so powerful, it was not natural, and he did not pause to think that it was because of his caress that his body had acquired such enormous power, so angry he was. It also did not occur to him that the infant did not act out of choice and as such was not responsible for what had happened. His anger might have been due both to the pain he had suffered, and the humiliation he might have felt on having fallen unconscious by being hit. Here was a small, arrogant man who misused his power in a most deplorable manner. Apart from this, Vyasa's conduct was well above reproach in Sarala's text. But this one grievously unjust act far outweighs a lifetime's good deeds done; it led to a totally meaningless engagement between Duryodhana and Bhima.
The man never repented even once for his despicable act, an act for which there are hardly any parallel in Saaralaa Mahaabhaarata. He never suffered disgrace in the unjust world; he did not suffer disgrace in his own eyes. Moral order is never more strongly violated than when men of learning and spiritual attainments and stature abuse their power against totally helpless victims. And often there is no redress. Krishna did not put duti krushna in place!