For an indefinite period from here on，mankind is going to advance cautiously，and consider itself lucky that it can advance at all.
分子分析：
主干：…mankind is going to advance cautiously, and consider itself lucky …
修饰成分：
for an indefinite period from here on 时间状语修饰整句话
that 引导从句修饰lucky
重难点词汇
mankind n. 人类
for an period from here on 从现在起的一段时间内
indefinite adj. 不确定的，无限的
advance vi. 前进
cautiously adv. 小心翼翼地
参考译文
在今后的漫长的时间内，人类将谨慎前进，而它感到幸运的是它确实能够前进。
今日赠言：
Behind every successful man there's a lot of unsuccessful years.
- Bob Brown
每个成功者的后面都有很多不成功的岁月.
鲍博.布朗
I think success has no rules, but you can learn a lot from failure.
- Jean Kerr
我认为成功没有定律,但你可从失败中学到很多东西.
静.科尔。
