It is clearly true, and not at all silly, that some facts in articles do not need sources to be given. However, the criterion "widely accepted" suggested here is not enough. For a fact to not need a citation it should be widely accepted, uncontroversial, and very easy to check. The last criterion is maybe the important one.

For example, if an article mentions Paris as the capital of France then it does NOT need to cite a geography book as verification that Paris is indeed the capital of France. Similarly, an article should be able to refer to the revolution of the Earth around the Sun without citing an astronomy journal.

Zero.

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