You can predict that 4% of photons will bounce back off a glass pane rather than cross through it, but you can never look at any individual photon and say whether this particular photon will go through or bounce back. All you can say is that if there are 99 other photons along with it, streaming towards a glass pane, 4 will bounce off and this photon may or may not be one of those. But the photon itself and it's own will, inevitably determine whether it goes through or not.