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!"