The phrase 'grass is always greener on the other side' is used to say about individuals who are never happy with what they have and they constantly ponder if others have it better.
Example in use: "Our bookkeeper always imagined that the grass is greener on the other side. She quit her job to pursue a legal education. However, she is still trying to find herself in the practice of corporate law."
This idea for this phrase comes from the livestock who, while grazing keep on looking for greener grasslands.