This week’s episode is called “The Three Hardest Words in the English Language.” (You can subscribe to the podcast at iTunes, get the RSS feed, or listen via the media player above. You can also read the transcript, which includes credits for the music you’ll hear in the episode.)

So what are the three hardest words? Conventional wisdom suggests: “I love you.” Readers of this blog recently offered up their suggestions of challenging three-word phrases. In their new book Think Like a Freak , Stephen Dubner and Steve Levitt tell us that the hardest three words in the English language are “I don’t know,” and that our inability to say these words more often can have huge consequences.

On this week’s podcast, we explore where this unwillingness to say “I don’t know” comes from. Dubner talks to Amanda Waterman, a professor of developmental psychology at the University of Leeds. Much of her research (gated papers here and here) is about people’s unwillingness – especially children’s unwillingness – to say “I don’t know.” Waterman has found that the vast majority of kids pretend they know the answer to unanswerable questions.

WATERMAN: It has varied between studies, but you’d be looking at two-thirds to three-quarters of children—and we’re talking in the age range here of about five to eight years old—would say ‘Yes’ or ‘No’ to a yes/no question that we know they don’t know the answer to.

Apparently this is a habit that we adults don’t grow out of. You will hear Levitt tell Dubner that he has witnessed people’s reluctance to say “I don’t know” way too often:

LEVITT: So we wrote Freakonomics, and because it was deemed a business book and we sold a lot of copies, that made us business experts. And since we wrote that book I’ve been asked a ton to go talk to companies and give them advice. And what’s amazing to me is I could count on one hand the number of occasions in which someone in a company, in front of their boss, on a question that they might possibly have ever been expected to know the answer, has said “I don’t know.” Within the business world, there’s a general view that your job is to be an expert. And no matter how much you have to fake or how much you are making it up that you just should give an answer and hope for the best afterwards. And I have seen it teaching the business school students, that they are incredibly good — the MBAs — at faking like they know the answer when they have no idea.

Levitt goes on to tell the story of one multinational retailer he worked with whose inability to admit they didn’t know ended up costing them millions of dollars. Finally, you’ll hear his suggestion for how we can all get better at saying these three most difficult words.