You can never reach the end of a rainbow because it moves as you move.

A rainbow is not a localized object but an angular phenomenon that depends on the position of the observer, the sun, and water droplets. According to the National Center for Atmospheric Research, rainbows are formed when sunlight enters a raindrop, reflects off the back of the drop, and refracts as it exits. This process happens at a specific angle of approximately 42 degrees relative to the observer's line of sight.Because this 42-degree angle is fixed to your eye's perspective, the 'circle' of the rainbow moves as you do. If you walk toward a rainbow, the droplets that were creating the colors for you are no longer at the correct angle, and new droplets further away take their place. This creates the illusion that the rainbow is retreating at the same speed you are advancing.Sir Isaac Newton first mathematically described the optics of rainbows in his 1704 book 'Opticks,' explaining how different wavelengths of light bend at different angles. Since the center of a rainbow is always directly opposite the sun from your eyes, two people standing in different spots will actually see two slightly different rainbows. This geometric requirement means it is physically impossible to ever reach the 'end' or see a rainbow from the side.