I read an article today on the Huffington Post that explained the question of Why are we here? by simply saying we are here because we decided to be. Our existence and reality lies in our consciousness. It's a new theory called Biocentricism and challenges the concepts of both God and Evolution aka the Big Bang Theory. Here is an excerpt:
"Indeed, according to biocentrism, it's us, the observer, who create space and time (which is the reason you're here now). Consider everything you see around you right now. Language and custom say it all lies outside us in the external world. Yet you can't see anything through the vault of bone that surrounds your brain. Your eyes aren't just portals to the world. In fact, everything you experience, including your body, is part of an active process occurring in your mind. Space and time are simply the mind's tools for putting it all together.
Theoretical physicists Stephen Hawking and Leonard Mlodinow recently stated:
There is no way to remove the observer -- us -- from our perceptions of the world ... In classical physics, the past is assumed to exist as a definite series of events, but according to quantum physics, the past, like the future, is indefinite and exists only as a spectrum of possibilities.'"
This is very similar to the idea in the book and movie The Secret about the Law of Attraction and how we attract things into our life by our thoughts. It's also very similar to Eckart Tolle's idea in The Power of Now about the concept of time being an illusion. As with psychoneuroimmunology, our thought process, attitude and state of mind have more control over things in our life (i.e. health) than we have generally, previously believed.
With that said I'd replace "Have a nice day!" with something like "Think nice thoughts!"