0 sad -- 憂鬱的,憂傷的
1 sadness that lasts for a long period of time, often without any obvious reason -- 憂鬱,憂傷
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。