It's bits and bytes. The 1 will stay a 1 and the 0 will stay a 0. This means that every digital one-on-one copy of digital media is as good as its original.
However. The media suffers from the environment (heat, human sweat, fingerprints, little creatures, dust). On top of that as already mentioned before the media degrades over time. (UV radiation, human sweat is like acid, oxygen). And the media moves. Moving parts are never ever doing 100% exactly the same from previous movements.
To solve all that a little they introduced error correction. If you read wikipedia a little about crc and error correction schematics you'll know what it does. Bear in mind that a normal cd player already does thousands of error corrections per second, even on pressed media!
Unfortunately the error correction seldomly is 100% perfect. So sometimes a corrected error gets corrected wrongly, thus resulting in ... an error! (Try to reread this sentence five times! ).
That.. and only that.. gives glitches, errors and disturbances in the digital media.