99% of the time, Freezing, Sticking & Skipping is caused by dirt or scratches on the playing surface of the disc, there is no data on this surface. The data is inside the disc and is read by a laser and a sensor.

Failure occurs when the laser is deflected away from the sensor by a scratch (or dirt) on the playing surface.  Not all scratches cause this to happen.  Some don’t deflect the laser far enough for it to miss the sensor.

Scratches are commonly less than 0.1% the thickness of the entire disc which means that a disc can be repaired many many times before it would be too thin to play.