Economics

The system gets support because the economy is doing well, but what you really need is for people to be able to support the system in times of crisis. And to do that, you really need people to feel engaged, to have a measure of understanding of how things work, and that they're directly participating in the system.

Precisely. This is exactly my worry. History makes it very clear that nothing stays the same forever. Sooner or later any system runs into issues, whether internally or externally caused, and in order to survive a system needs to be robust and enjoy not just opportunistic but principled support. Capitalist societies unfortunately have gotten very good at ideologically priming their populations for accepting that the system cannot be changed no matter how bad their crises (which they inevitably and regularly run into) get. "There is no alternative" and all that. They invest heavily in ideological indoctrination and in justifying the system to the people, even if they have to constantly lie to achieve this. We are surrounded by it, we are drowned in pro-capitalist propaganda almost 24/7 from the moment we begin as children to learn how the world works until we die, through advertising, the media, the educational system, our social and work environment, etc.

Socialists could have such a great advantage in this regard because we don't need to lie, all we need to do is properly present the truth to the people. Reality is on our side. Yet we see so many socialist states that have failed or are failing to do that. The only one that seems to have done a better job on this than most is the DPRK (though i strongly emphasize the "seems" here because frankly i just don't have a very clear understanding of how things in the DPRK work or exactly how the people there are taught to think about their system... forming an opinion based solely on what defectors say, even ones who have since seen the ugly reality of capitalism and regret their decision, is not reliable), and perhaps to some extent Cuba, though i think it can be hard to distinguish between what is support for the social and economic system, and what is patriotism or the desire to protect national independence against imperialism. Not that the latter isn't also useful but it's not a reliable safeguard against counter-revolution.