“The grass is always greener on the other side of the fence.”
Meaning: People always think that other people’s lives or situations are better than their own, even though this is usually not the case. In general. people are never satisfied with what they have.
This can be used when advising a friend who is about make a drastic decision based on a dissatisfaction, which might end up being the same with the option they are considering. One may decide to quit their job and work for another company, expecting better conditions, but once they settle in, discover that their previous company was much better. You can prevent a friend from making such a terrible mistake by reminding them that the grass is always greener on the other side of the fence, and that they need to consider their options very carefully before abandoning what they have.