the grass is (always) greener (on the other side) idiom saying
（总是觉得别人的处境好）邻家的草分外青；这山望着那山高
something that you say that means that other people always seem to be in a better situation than you, although they may not be
I sometimes think I'd be happier teaching in Spain. Oh well, the grass is always greener on the other side! 我有时会觉得在西班牙教书会更开心。嗨，真是的，这山望着那山高啊。