Then, aged 35, sitting under a tree at the place now known as Bodh Gaya (south of Patna), he vowed to stay there until his goal was achieved.
He was confident that he could accomplish his goal. 
mnli hypothesis: He was confident that he could accomplish his goal.  premise: Then, aged 35, sitting under a tree at the place now known as Bodh Gaya (south of Patna), he vowed to stay there until his goal was achieved.