Why can’t you reach the end of a rainbow?
A rainbow is an optical illusion, not a physical object, so it doesn’t have a physical end point. Seeing a rainbow depends on the position of your eyes in relation to the Sun, so as soon as you start moving towards what you think is the end of the rainbow, it will move out of reach or disappear completely. It’s a bit like trying to walk to the end of your shadow; it will move as you do.
Seeing a rainbow depends on the angle at which sunlight hits raindrops in the sky