All of our experiences take place in our minds and are, as a result, virtual. When building experiences and products, we must recognize this, and ask ourselves "what is happening in the user's mind"? A word processor isn't actually a typewriter - it just plays one on your computer.
Fluidity and "naturalness" are important. Every action the user takes, or can take must feel natural, with minimal re-learning on their part. When we achieve this, then the user is drawn into the virtual world we have created for them.