A quote attributed to John Maynard Keynes, as a catch phrase in his rebuttal to laissez faire economics, as proposed by Adam Smith. The idea is that rather than "in the long run, everything will even out", that "in the long run, we're all dead", so we should aggressively push to rectify economic problems (within our lifetimes), rather than just letting everything work itself out.

If you're not into economics, and have fatalistic tendencies, you might just want to use this phrase wherever it fits; it tends to rile people up, which is always an enjoyable activity...