If the future is always brighter then you can borrow from it without fear.
Of course if you actually take a look at human nature and see its many flaws then you will be a bit more conservative in your borrowings.
Keyne's flaw may be that he viewed the openly libertine lifestyles of his friends in the Bloomsbury Group as a generally good thing. He was very wealthy himself so he could afford it. But can an entire country support a huge population of bohemians?
SanFranNan Pelosi thinks so. Remember her pimping of Obamacare saying "... you can be an artist and not worry about healthcare any more..."?