... or possibly from observation.
Star athletes aren't the only people who go to seed once they taste the big victory, it happens in other professions and to entire civilizations.
Take the United States for example. We reached the height of our power from 1945 through the 1960s before suffering a sharp 70s decline to the Vietnam War and the Oil Embargo. Then we made it back in the 80s by achieving victory over the Soviet Union before losing it in the Iraq War.
In the case of feudalism: the system developed to stop the -90% population drop from the decline of the Roman Empire. For a thousand years, they managed to keep the population about even before finally eeking out enough of a surplus that they had more humans than they needed farmers. The result was an increasing level of innovation that led to the formation of the first towns and trade guilds. That was the genesis of modern capitalism. It started as a bubble within feudalism, nurtered by feudalism's success, and then exploded outward to destroy feudalism.
It wasn't feudalism's failure that destroyed feudalism. Feudalism succeeded at its goal: reverse the population decline. Once that occurred, its relevance as an economic system faded away. Similarly, once the United States succeeded in destroying the Soviet Union, the other countries no longer needed us and stopped respecting our power. That's why we received minimal aid during the Iraq War.
In much the same way, the purpose of capitalism is to make it possible for individuals to acquire great wealth. Through corporations, it creates individuals who have so much money they can buy their way out of accountability, the way the banks did in the 2008 recession, or the way Donald Trump does all the time. However, capitalism depends on accountability. Once accountability is gone, you've replaced it with corporatism.
Real capitalism in the United States has been dying since the end of the Second World War, but historians will look back on 2008 as the final death.
