Handbags   (The sad, the bad and the ugly. Non-productive stuff here.)

We have had the nests robbed by hawks or crows in years past, this time I'm not sure in this case, there was one egg broken and it may be that because there was no formed young in the egg, the robin female may have abandoned the nest as a result. The other two eggs weren't damaged.
Predators are always on the lookout for eggs or more so newly hatched young.