expression, godan verb (-mu)
never satisfied with what one gets; always wanting more; give an inch and take a mile
A classical Chinese-derived idiom (故事成語) used to criticize insatiable greed or ambition. Literally refers to a historical figure who, after taking the Long region, immediately set his sights on Shu (Sichuan). Used in formal or literary contexts.
He just got promoted, but he's already aiming for the next position. It's exactly a case of never being satisfied with what one gets.
あの会社は市場シェアを拡大した途端、海外進出を企てている。隴を得て蜀を望むとはこのことだ。
As soon as that company expanded its market share, it started planning to go overseas. This is what they mean by giving someone an inch and having them take a mile.