The Other Man's Grass Is Always Greener...

It is of course perfectly natural to assume that everyone else is having a far more exciting time than you. Human beings, for instance, have a phrase that describes this phenomenon, ‘The other man’s grass is always greener.’

The Shaltanac race of Broopkidren 13 had a similar phrase, but since their planet is somewhat eccentric, botanically speaking, the best they could manage was, ‘The other Shaltanac's joopleberry shrub is always a more mauvy shade of pinky-russet.’ And so the expression soon fell into disuse, and the Shaltanacs had little option but to become terribly happy and contented with their lot, much to the surprise of everyone else in the Galaxy who had not realised that the best way not to be unhappy is not to have a word for it.

(Douglas Adams, 'The Hitch-hiker's Guide To The Galaxy')