The title comes from Thomas Gray's poem "Ode on a Distant Prospect of Eton College" (1768). The actual lines (the last two lines of the poem) are ".... Where ignorance is bliss, /'Tis folly to be wise".
The original 1949 play by James Bridie, under the title 'It Depends What You Mean', enjoyed a great success with Alastair Sim as the director as well as the leading man. It opened in Glasgow's King's Theatre on September 11 1944 with a cast including Angela Baddeley and Wilfred Hyde-White. The production then toured Aberdeen and Edinburgh before beginning a long run at the Westminster Theatre, London in October. Sim worked closely with Bridie on many projects and was able to use his box-office appeal to bring many, like this, to screen and also to television.