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).