Learning takes us through many states of life, but it fails utterly in the hour of danger and temptation. Then faith alone saves.
A fast to be true must be accompanied by a readiness to receive pure thoughts and determination to resist all Satan's temptations.
When there is no desire for fruit, there is also no temptation for untruth or himsa.
Hinduism would not have been much of a religion if Rama had not steeled his heart against every temptation.