We have two classes of forecasters: those who don’t know and those who know they don’t know.

John Kenneth Galbraith (1908-2006) Canadian-American economist, diplomat, author

(Attributed)

Variants:

• There are two classes of people who tell what is going to happen in the future: Those who don't know, and those who don't know they don't know.
• You can divide the world into those who don't know and those who don't know they don't know.
• There are those who don't know, and there are those who don't know they don't know.
• We have two kinds of forecasters: Those who don't know ... and those who don't know they don't know.
• There are two kinds of economists: those who don't know the future, and those who don't know they don't know.