Hi stanley, " one man gathers what other man spills" - this means that when a person discards or throw away something that is not important to him, other people try to get it because they need to use it or its important to them.

我试试用华语来讲解。 意思就是说一个人要倒掉不须要的东西却是另一个人的所需。比较清楚了吗？