A pendant is the piece most often lost and least often repaired in time. The clasp takes the load; the chain takes the friction across the collarbone; the setting takes the knocks.
Take the necklace off before sleep, before a shower, and before anything that involves a strap across the shoulder. Store it flat in its pouch rather than hanging on a hook, where the chain will stretch.
Once a year, have the links and the setting checked. It costs less than replacing the piece.