Infallibility?

 Rambam (Letter on Astrology): I know of course that it is possible to search and find isolated opinions of some sages in the Talmud and Medrashim whose views contradict what I have said. ... These statements should not trouble you because one doesn’t simply discard a clearly established halacha and revert back to the initial analysis. Similarly it is not appropriate to discard a well validated principle and simply rely on a minority opinion of the sages instead. That is because the sage is not infallible and might have erred by overlooking some important facts or hints when he stated his views.