The history of Western science confirms the aphorism that the great menace to progress is not ignorance but the illusion of knowledge.

Daniel J. Boorstin (1914-2004) American historian, professor, attorney, writer

Speech (1992-08-31), “Realms of Discovery, Old and New,” World Space Congress, Washington, D.C.
    (Source)

Collected in his Cleopatra's Nose: Essays on the Unexpected, Part 1, ch. 1 "The Age of Negative Discovery" (1995).

In Carol Krucoff, "The 6 O'Clock Scholar," Washington Post (1984-01-29), he is quoted:

The greatest obstacle to discovery is not ignorance -- it is the illusion of knowledge.
 

See Billings (1874).