The story started with the Senior Monk and his young Novice on their visit to a Venerable of another monastery.
Their journey was a long and arduous one, requiring them to cross a fast-flowing stream and two mountains. When they were approaching the stream, they saw a lady trying to cross over to the other side, but was afraid of the fast-flowing waters. The Novice wanted to carry the lady over to the other side, but the Monk stopped him, and piggy-backed the lady across the stream himself instead.
Upon crossing the stream, the Monk and the Novice bade the lady farewell. The Novice was extremely annoyed. He thought, "Monks are supposed to keep a distance from the opposite gender, but that lecherous monk stopped me and ferried her over himself instead !" The more he thought about it, the angrier he became.
Finally, the Monk and the Novice crossed the two mountains and were approaching the monastery. Unable to contain his anger anymore, the Novice burst out his frustration to the Monk. The Monk replied, "All I did was just piggy-back the lady across the stream. I harboured no desires or lust, but you were not ready yet. By the way, I have let go of the lady by the stream, but why have you been carrying (the thought of) her across the mountains, and all the way to this place ?"
The Novice realised his foolishness and was enlightened. Upon reaching the monastery, the Novice dedicated his time eradicating the Three Poisons (ignorance, aversion and lust/greed), overcame craving & attachment, and became a very good monk.
Source : dharmmasara.web
Source of picture : web