Answer: The phrase "the grass is always greener on the other side" means that people tend to believe that other people or places are better than their own, even though they may not actually be so.
Explanation: It's a metaphorical way of saying that we tend to be envious of what we don't have and often think that our current situation is not as good as what others are experiencing. It's a reminder to be grateful for what we have and not to take things for granted.