There are many other excellent or more suitable people, things, opportunities, or possibilities in the world that one may find. Said especially if someone has recently been through something or some romantic relationship that has failed or turned out badly. I know you are broken up about Janet leaving you, but there are plenty more pebbles on the beach. I'm pretty disappointed that I didn't get the job, but I'm trying to remind myself that there are plenty more pebbles on the beach.