0 a small hole in a door or a wall through which you can look, especially without being seen -- (門或牆上的)窺視孔;貓眼
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。