0 something that tricks your eyes and makes you think you see something that is not really there, or see it differently from how it really is -- 視錯覺；光幻覺
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。
