Money is like manure: it's not worth a thing unless it's spread around encouraging young things to grow.
The real sting here isn't that wealth should be generous—plenty of people agree with that platitude. Rather, Wilder's suggesting something odder: that money sitting idle isn't merely selfish, it's *sterile*, literally worthless as a psychological or moral fact. A miser with a vault full of gold has precisely nothing, because wealth only becomes real through its movement, its generative capacity. When a grandfather funds his granddaughter's violin lessons or a business owner invests in an apprentice's wages, the money transforms into something alive—and only then does it matter at all.