A persuasive case for a bold decision isn't the same as a reliable plan. The Athenian expedition to Sicily is a memorable example of how a democracy can listen to arguments and still make a catastrophic choice.
In 415 BC, Athens approved a major expedition against Sicily. Alcibiades supported it; Nicias warned against it. In Thucydides' account, Nicias later tried to discourage the venture by explaining the scale of the force it would need. The effect was to encourage a larger commitment.
That detail matters. The problem wasn't that nobody objected or that the assembly never reconsidered. It was that the objections didn't produce the caution Nicias intended.
What happened after the decision
Alcibiades was recalled and fled rather than return to face proceedings. Nicias remained among the commanders. The campaign failed, and the Athenian force was destroyed in 413 BC. The eclipse that influenced the decision to delay withdrawal is one striking part of a much longer military and political failure.
No short analogy can explain the whole disaster. It certainly wasn't simply a good speech followed by inevitable ruin. Decisions, resistance and mistakes continued after the fleet sailed.
What the story does challenge is the assumption that public enthusiasm or a thorough debate guarantees sound judgement. People can hear a warning and interpret it as a reason to commit more resources.
Let a proposal survive difficult questions
That isn't a case against democracy or ambitious policy. Refusing every risk can be disastrous too. It is a case for requiring a proposal to explain what could go wrong, what would make us reconsider and whether the people carrying it out have a workable plan.
A timetable, a cost estimate and an account of the likely opposition may be less exciting than the promise. They are part of judging whether the promise is credible.
A government should be able to answer those questions before an enthusiastic audience becomes a reason to stop asking them. Athens doesn't tell us to reject every bold speaker. It gives us a reason to listen carefully to the person describing the risks, including when the room would rather hear something else.