To the disbelievers and downvoters this is true. I was going to say it stems from Abrahamic tradition, and biblical use as a period of trial, but Wikipedia tel

To the disbelievers and downvoters this is true. I was going to say it stems from Abrahamic tradition, and biblical use as a period of trial, but Wikipedia tells me "The number 40 is used in Jewish, Christian, Islamic, and other Middle Eastern traditions to represent a large, approximate number", with some other older traditions shown. https://en.wikipedia.org/wiki/40_%28number%29 https://en.wikipedia.org/wiki/40_%28number%29 Presumably Pratchett's inspiration for the Troll number system (many-many-lots) :)