One day, a fish came to visit some kangaroos. He saw right away that the kangaroos spent all their time hopping on the dusty ground and browsing among the shrubs. Their habits would never work, and surely lead to their deaths, if they were to come to the ocean reefs even for a single month!
"Foolish kangaroos," he called to them, "heed my words and live! This hopping and browsing is pointless madness! You must learn to paddle and snatch live prey from among the rocks! The ocean is no place for hopping air-breathing creatures, so come follow me and learn the better way!"
The kangaroos, amazingly well-adapted to their un-ocean-ly environment, dutifully ignored the fish. They looked for common ground for conversation, but somehow the topic always turned to the futility of hopping and the unpleasantness of a dry environment. Sometimes they asked polite questions, and the patient among them tried to explain that their way of life was forever on solid ground where browsing and hopping are pleasant and efficient. They explained that attempting to swim in the dust and snatch prey with their teeth would be as foolish for them as it would be for the fish to hop and browse.
The kangaroos stubbornly refused to follow the fish, despite his superior sea experience.