It has been proposed to solve the energy crisis on earth by exploiting helium-3 on the moon. Helium-3 can be used as fuel in fusion reactors. This proposal is absurd. Even if man can mine helium-3 on the moon, it will be at least 50 years later to build the fusion reactor. It will be too late to solve the energy crisis facing the earth today.
The best summary of the meaning of the stem is that if the energy crisis facing the earth today cannot be solved within 50 years, it will be too late.