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
❍ 地势便利，其以下兵于诸侯，譬犹居高屋之上建瓴水也。(《史记·高祖本纪》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
～，势如破竹press on irresistibly like splitting a bamboo
高屋建瓴ɡǎo wū jiàn línɡ
建：倒水、泼水；瓴：指盛满水的瓶子。在高高的屋顶上向下倒出瓶里的水。比喻居高临下、锐不可挡之势。operate from a strategically advantageous position, at a commanding height, be strategically situated