All propaganda must be popular and its intellectual level must be adjusted to the most limited intelligence among those it is addressed to. Consequently the greater the mass it is intended to reach, the lower its purely intellectual level will have to be… The receptivity of the great masses is very limited, their intelligence is small, but their power of forgetting is enormous. In consequence of these facts, all effective propaganda must be limited to a very few points and must harp on these in slogans until the last member of the public understands what you want him to understand by your slogan.
The above excerpt is from Adolf Hitler’s Mein Kampf (1925/26). Richard J. Evans quotes it in The Coming of the Third Reich (2003; p. 168), along with this: “The people in their overwhelming majority are so feminine by nature and attitude that sober reasoning determines their thoughts and actions far less than emotion and feeling.”