One of the painful things about our time is that those who feel certainty are stupid, and those with any imagination and understanding are filled with doubt and indecision.
This is from a radio address presented by Russell in 1953, “Present Perplexities,” part of his radio series, “Living in an Atomic Age.” You can hear Russell read that line here, in the sample on the right, or at YouTube, at about the 4:20 mark. The essay is printed in various collections, usually under the title “Current Perplexities.”
I came across this quotation of Russell while listening to a speech (in a debate) by Stephen Fry, who introduced the quotation by saying: “I would like this quotation from my hero Bertrand Russell to hover over the evening” (see here, 36:10 mark). After he reads the quotation, Fry exclaims, “Let doubt prevail!”
But it seems that Fry has undermined the point that his hero was trying to make. Russell's comment was not a criticism of certainty; it was a lament that in his day it seemed that only stupid people enjoyed certainty. It is worth noting that Russell considered this aspect of his time “painful,” and he immediately follows the section quoted with the words, “I do not think this is necessary.” He goes on to exude certainty with the intention of overcoming the “present perplexities.” Russell more-or-less exclaims, "Let certainty (for smart people) prevail!"
Of course, both Fry and Russell are complex thinkers whose views cannot be boiled down to a single battle cry. But it is interesting how a lament from Russell became a precept for Fry.