I came across the old footage of the 1939 World’s Fair, which was promoted, at the time as “the world of tomorrow“, talking about the magnificent world of twenty years from now, of 1960!
Ironically, this fair co-incided with the outbreak of World War II, but in my opinion, the optimism within did prevail longer, probably up until the 1970s (there was a follow-up fair in the mid-1960s!).
There is an immensely positive message here, of how the future had to be better.
When people talk about how “it’s time to build” again, I think this — recapturing this lost optimism — is the only way to mean it in an unambiguously good way.