That bit about the cookie being.....right.....there! Why on earth would your puppy give you direct eye contact when he could be looking at the cookie?
This game teaches your puppy to look at your face instead of the cookie. The concept that working on the cookie directly will not make it become available is a difficult one! But really, teaching this concept is only a matter of well-timed clicking and treating.
You can show your puppy at a very young age how powerful it is to choose to "work for a living." Your puppy will learn here that offering behaviors that earn the click is how to make that cookie right there become available.