The Condorcet Jury Theorem

"If each member of a jury is more likely to be right than wrong, then the majority of the jury, too, is more likely to be right than wrong; and the probability that the right outcome is supported by a majority of the jury is a (swiftly) increasing function of the size of the jury, converging to 1 as the size of the jury tends to infinity."
Nicolas de Condorcet, 1785.
Quoted in "Epistemic Democracy: Generalizing the Condorcet Jury Theorem" by Christian List