The grass being greener comes from the optical illusion created by distance. If you stand in your neigbours yard and look at your own it will look lovely. Look down at your feet and you'll see termites, twigs and bald spots all over his yard.

Exodus 20 - Do not covet.

Saint Paul somewhere paraphrased - I have had good times and I have endured hard times and have learned to be content in all things.

This way the grass is always greenest right where you're at.