In spite of these successes, Feynman, in his 1963 undergraduate lecture that discussed the spin-statistics connection, says: "We apologize for the fact that we cannot give you an elementary explanation." Neuenschwander echoed this in 1994, asking if there was any progress spurring additional proofs and books. Neuenschwander's 2013 popularization of the spin-statistics connection suggested that simple explanations remain elusive.