The theme is that life can be hard but you'll get through it. An example of this in the song would be when Kacey sings "And you're stuck out in the same old storm again,you hold tight to your umbrella, but darling, I'm just tryin' to tell ya, that there's always been a rainbow hanging over your head". It is evidence because the rainbow over your head represents that you will get through the tough times. The "storm" refers to the tough times.
