0 A once-in-a-lifetime experience or opportunity is very special because you will probably only have it once. -- 一生中难得一次的;千载难逢的;难能可贵的
A tour of Australia is a once-in-a-lifetime experience. 澳大利亚之行是一生难得的一次经历。
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。