ETA: It is always the case in science that we don't know what we know until we know it. There are numerous scientific theories that were once accepted a fact, and in which any and all suggestions that the science might be wrong were dismissed out of hand by establishment scientists until the evidence became overwhelming that the science was wrong. Examples include Spontaneous Generation, Lysenkoism, Vitalism, Matrnal Impression, Preformationism, the existence of Phlogiston, Caloric Theory, Electrochemical Duelism, Lumininiferous Ether. In physics, the atom has undergone huge theoretical and model changes - Dalton's model, Thomson' model, Rutherford's model, Bohr's model, the Electron Cloud model. All of these at one time held sway. Many scientists dismissed challenging theories out of hand. Every one of the above, and more, turned out to be wrong.
This is why Sagan refers to science as a "self-correcting process" - the pity is that some scientists are not on board with this philosophy; they would rather protect their reputations.