Close to the planet, the planet's gravity prevents the particles from pulling themselves together. The boarderline distance which separates the regions where rings exist from the region where satellites form is called the Roche Limit . Planetary rings are always found inside the Roche Limit. Sometimes satellites can be found inside the Roche limit. Their internal cohesive forces can resist tidal disruption.
Rocks can resist tidal disruption.
Rubble piles cannot. Ring particles in the gap orbit twice for every one orbit of Mimas. The same process may create gaps in the dust debris disks surrounding stars with planetary systems.