Simply put, to see a rainbow you need the sunlight behind you and the rain in front of you (because physics). But do you know why I like rainbows?
They highlight the fact that from challenge can come great beauty;
That no two rainbows are alike as they are observer dependent (the rainbow I see over Hyde park differs to the one you see from Grosvenor Square).
You see them by looking up not down and;
Despite having no practical purpose whatsoever, are generally remarked upon by all that see them.