0 (the quality of often having) a sudden and usually silly wish to have or do something, or a sudden and silly change of mind or behaviour -- 異想天開;反覆無常;突發奇想
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。