We expressly warn him against giving way to any kind of motive which would cause him to select from or to exclude any of the ideas (associations), whether because they are too ‘disagreeable,’ or too ‘indiscreet’ to be mentioned, or too ‘unimportant’ or ‘irrelevant’ or ‘nonsensical’ to be worth saying.
Freud’s most direct formulation of the fundamental rule of free association, establishing non-selective verbal disclosure as the technical foundation of psychoanalytic treatment and framing resistance to it as clinically diagnostic.
, Introductory Lectures on Psycho-Analysis, 1917thesis