Between the death of Domitian and the accession of Commodus, there was a period of stability and prosperity, at least for patrician Romans (Pax Romana). At the time, people looked to the past for what was best. They felt the future "would be at best a weariness, and at worst a horror" (Bertrand Russell). Marcus Aurelius, who was the last emperor of the period, said the "Gospel was one of endurance rather than hope." Thought shifted towards enduring fate rather than reshaping it.
Earlier — during the 3rd century BC — the philosophy represented misfortune-minimization rather than fortune-maximization (Epicurean ataraxia and Stoic apatheia).
Several factors maintain the long-run "healthy" balance between pure democracy and pure oligarchy (legitimacy, capital, administration, progress, etc). The health of the balance is ultimately determined by the scarcest factor, often progress.
In both of the cases above, high cultural achievement + stability gave the appearance of strength but underlying growth drivers (new tech, productivity leaps, resource expansion) slowed or stopped. Hope seems to be a nontrivial driver of progress.
The smartest people today focus on misfortune-minimization. Effective altruism stood out to me in high school, enough for me to BART up to a Berkeley EA meeting and idolize SBF's Alameda Research. Effective altruists speak of existential risk reduction. A few things could wipe out humanity: misaligned AI, nuclear war, climate change, genetic-engineered pathogens, etc. Dedicating your time and capital to minimize these risks seems smart, whatever scenario maximizes the EV.
But instead of misfortune-minimizing, why not fortune-maximize? (e.g. by building more energy, technology, etc.) The probability of prosperity seems much more likely with effort focused on the up and not the down. American ambition has slipped heavily, even though it still leads the world for some reason (idk why... Protestantism/Calvinism?). We went from dreaming about harvesting stars for energy in 1960 to DoorDash via drones today. Peter Thiel famously said "we wanted flying cars, instead we got 140 characters," even though he was the first funder of Facebook. Just like Marc Andreessen who prophets e/acc but is an Atherton NIMBY.
Our late-stage imperial position may make this mentality is inevitable/self-fulfilling, pushing our imbalance towards oligarchy further. If we keep optimizing for survival over expansion, decline becomes inevitable. The only way out is to reverse our human nature, by making fortune-maximization the cultural default.