How funny. Why do I believe I'm alive?
Literally, because I can see myself breathing. Because people tend to look at me and speak back to me when I speak to them. This lets me believe I’m alive, and not a ghost flitting about. I’d think those are both fairly obvious signs of my aliveness. There are more, lots more, but I think I’ve made my point.
Metaphorically (which, I guess, is what they're aiming for here) , I think I’m here to do my bit. To live, laugh, and love as much as I possibly can, leaving behind only good things when I go. Before I start sounding like a self-help book, let me stop there.