[Idiom] People always want what they don't have

[Keith Kelly]

A Bulgarian friend asked me recently what the equivalent in English would be for:
'Гладна кокошка просо сънува' (gladna kokoshka proso sanuva)
which translates literally as 'a hungry hen dreams of seed'.
In English this comes across in usage as 'people always want what they don't have'.
So, it's less to do with 'hunger' than to do with desire for something you see but don't have.
Any suggestions?
Thanks.

 

[Tdol]

How about The grass is greener on the other side of the fence?