The End of the Rainbow

Looking up at the rainbow after the rain, do you think of the beautiful fairy tale of childhood: at the end of the rainbow is a bucket of gold. When you grow up, you realize that rainbows are refracted by small water droplets in the sky, and the end of the rainbow will disappear where there are no water droplets, but we can't see it. But since we can't see the end, how can we know? Maybe there are some unknown secrets there...