The “purposive” man is always trying to secure a spurious and delusive immortality for his acts by pushing his interest in them forward into time. He does not love his cat, but his cat’s kittens; nor, in truth, the kittens, but only the kittens’ kittens, and so on forward forever to the end of cat-dom. For him jam is not jam unless it is a case of jam to-morrow and never jam to-day. Thus by pushing his jam always forward into the future, he strives to secure for his act of boiling it an immortality.
Helpfully, there is a Wikipedia page on the “jam tomorrow“. It turns out that the jam reference comes from Lewis Carroll’sThrough the Looking Glass (1871), in which the White Queen offers Alice to work in exchange for jam that she (Alice) will always receive tomorrow, i.e. never. Back to Keynes: Such forward-looking behavior is helping to solve the economic problem, but as soon as that is done (it will take at least 100 years), we can stop pushing the jam into the future.
(And presumably start eating it, though Alice says she does not care for jam, but perhaps that is another story.)
Ragnar Frisch in the early 1960’s had high hopes for future Soviet economic development:
The blinkers will fall once and for all at the end of the 1960s (perhaps before). At this time the Soviets will have surpassed the US in industrial production. But then it will be too late for the West to see the truth. (Frisch 1961a)
Discussing economists’ reliance on measures of growth and GDP, Joel Mokyr asks:
So you go to somebody who is about to have surgery and you ask him, How much would you demand to be paid if I took out your appendix without anesthetizing you, without putting you to sleep? Nobody would agree. The sum would be infinite. What can anesthesia contribute to GDP when it was introduced in the 1850s and 1860s? Russ:Could not be very much. Guest: Nothing. It’s very small. But that is exactly the kind of thing we fail to account for in our calculations. So that’s why I gave that whole list of things; and we could make this list infinitely large. It is the small things that actually don’t amount to an awful large part of our income and product that actually have improved life a great deal and that we really wouldn’t want to do without any more.