Original phrase: You’ll earn less building rockets than you’ll earn selling eggs
It's 搞导弹的不如卖茶叶蛋的. It's usually used to describe 脑体倒挂, the special social phenomenon in 1980s and 1990s at Mainland China.


  脑体倒挂是指相同条件下脑力劳动者的报酬低于或等于体力劳动者取得的报酬数量。


[ 脑体倒挂 means under same condition, mental workers' income is less than blue-collar workers'. ]