The meaning of "life is beautiful" really just means that the act of being alive is beautiful. That if you stop and look around once in awhile you might realize that life is too short to have road rage or always have a short temper. There's just no need for it. Take what you have and make it how you want to see it. If it's not beautiful, change it.
Nikki Sixx really puts meaning into all this. He was once a drug addict and is now a photographer and a better band member because of this quote. He has realized that he can die and that life is too beautiful to waste on doing foolish things such as drugs.
To me, this quote tells me that when I think that I'm having a bad day, I'm still alive. Every situation could be worse and I'm lucky to be where I am.