"With a model, a light can hit it a certain way or you can find a new camera angle and have that 'happy accident', but with CG, you have to plan for that accident."
To me, that's the problem with CG in a nutshell. All the optics and physics that we take for granted and happen naturally in the real world have to be consciously and purposely accounted for, calculated, adjusted and balanced in the computer. There's just too much of that, and too much interaction between them, for CG to come off as fully 100% indistinguishable from reality, at least under current limitations of programming. Even if you can't figure out WHY, you can usually sense when something is CG and when it isn't.