Over time settings can wear away. Rubbing occurs with normal wear and if you are not careful you can lose a stone when a claw setting has worn thin or completely worn off.
If you have expensive stones or lots of little stones you need to pay attention to your settings.
The first thing you can do is learn to hear a loose stone by tapping the stone with your nail and listening for clicking or jingling sounds. If the stone is loose you will be able to hear it move when you tap it.
This is a good first line of defense for checking your stones and their settings.
Next, look at the metal holding the stones in place in your jewellery. If it is a claw setting look at the balls on top of the claws holding the stone. There should be at lease .5mm thickness of metal on each claw. If the claws look completely flat or if the ball is missing, it needs to be re-tipped.
If your stone is set in a bezel, (a rim of metal around the top of the stone) look for racks in the metal around the stone. A bezel setting is the strongest setting and will show less wear than other types of settings.
Finally, make sure all your settings are fully touching your stones and have no sharp edges. A good rule is the nylon test. Run a nylon stocking across the setting and if it snags anywhere, it needs some work by your local goldsmith.
’20 Tips on maintaining our Jewellery’, Gillian E. Batcher, 2013