pour water off a steep roof—sweep down irresistibly from a commanding height; stand on a vantage point and have a farsighted(/commanding) view; be strategically situated;operate from a strategically advantageous position
? 地勢便利，其以下兵于諸侯，譬猶居高屋之上建瓴水也。(《史記·高祖本紀(jì)》382) From such an advantageous stronghold,sending forth troops to subdue the feudal lords is as easy as standing on a roof and pouring down water from a jug.
高屋建瓴
pour water off a steep roof—sweep down irresistibly from a commanding height;operate from a strategically advantageous position
～，勢如破竹press on irresistibly like splitting a bamboo
高屋建瓴ɡǎo wū jiàn línɡ
建：倒水、潑水；瓴：指盛滿水的瓶子。在高高的屋頂上向下倒出瓶里的水。比喻居高臨下、銳不可擋之勢。operate from a strategically advantageous position, at a commanding height, be strategically situated