0 If a ceiling, roof, or other structure caves in, it breaks and falls into the space below. -- 塌陷;坍塌;塌方
1 to cave verb -- 讓步;屈服;妥協
We can complete it step by step however long the road is and it can't be completed however short the road is if you don't even mark your footprint.
再长的路,一步步也能走完,再短的路,不迈开双脚也无法到达。