[Nagel] did propose to me as a separate project the reading of W.V. Quine's proof of the completeness of propositional logic, that had appeared [...] in the Journal of Symbolic logic. This was a stupendous experience in my education, now because of the subject of the paper, but because it showed me vividly that new work in logic and more generally in mathematics, was being published, and that---with great difficulty---I could read and follow it. [...] As to the concept of completeness which was the focus of Quine's paper, it did not get through to me. I simply noted that the aim of the paper was to show that every tautology had a formal proof in the system of axioms presented, and I expended my utmost effort to check Quine's reasoning that this was so, without ever reflecting on why author and reader were making this effort. This strictly limited objective also kept me from wondering how the author thought of putting the steps of the proof together; the result was that I failed to get "the idea of the proof," the essential ingredient needed for discovery.
Leon Henkin, The discovery of my completeness proofs
