True democracy has never really been tried
All the so-called 'democracies' we've seen throughout history have been flawed and corrupted versions of the ideal. Real democracy means every single person having an equal say in every decision that affects them. But what we have are representative republics where the masses vote for leaders who then make choices on their behalf.
That's not true democracy - it's an oligarchy disguised as democracy. The ancient Athenians had a more direct form of democracy, but even that excluded women, slaves, and foreigners from participating. No society has ever achieved a pure system where all people truly govern themselves collectively on all matters.
Until we do, we can't say democracy has succeeded or failed. It has never existed in its perfect form."