Reply #15: The trouble is that your brain has been trained through millions of years...

[Tesha]

...of evolution and all the real-world experiences
of your life that the focus of your eyes and the
turning-inwards of your eyes are related: when an
object is close to you, your eyes must not only
focus more-closely but they must turn inwards more.

3D movies on a flat screen break that assumption;
your eyes have to hold focus at (essentially)
infinity even if the object appears to be 6"
from your nose.

Someday, true holographic (volumetric) displays
won't have that problem but right now, no practical
large-scale realizations of such things exist (a
few small-scale true-volumetric displays have been
built).

Tesha