Portraits - subject looking away from camera

I've really become hyper-aware of posed photos where the subject is looking somewhere other than at the camera.
In some shots, it looks perfectly natural and lends a positive "captured in the moment" effect. In others, it is annoyingly obvious that the subject is posed and is just following the instruction to "look away". They have a very unfocused and unrealistic look on their face which, in my opinion, makes for a horrible photo.
What I'm not clear on is what makes the difference, and if it can be managed. Is it as simple as having the subject actually look at something - focus on something specific as opposed to just gazing at nothing? Or is it that some models look natural and others simply don't, no matter what you tell them to do? I've seen one on here who always has the "deer in the headlights" look, so it might just be an individual thing...
Thoughts?
In some shots, it looks perfectly natural and lends a positive "captured in the moment" effect. In others, it is annoyingly obvious that the subject is posed and is just following the instruction to "look away". They have a very unfocused and unrealistic look on their face which, in my opinion, makes for a horrible photo.
What I'm not clear on is what makes the difference, and if it can be managed. Is it as simple as having the subject actually look at something - focus on something specific as opposed to just gazing at nothing? Or is it that some models look natural and others simply don't, no matter what you tell them to do? I've seen one on here who always has the "deer in the headlights" look, so it might just be an individual thing...
Thoughts?