From the transcript:

Stephen Dubner is interviewing Scott Lilienfeld, a professor of psychology at Emory University.

DUBNER: And the last one weâ€ll do right now is “steep learning curve.”

LILIENFELD: A lot of people will say, “Oh, I started on a new job where I was having to do something new. And this job has a really steep learning curve.” In fact theyâ€re getting it backward. A steep learning curve is easy. Because a steep learning curve means —

DUBNER: You learn a lot in a hurry, right?

LILIENFELD: Not slowly.

DUBNER: When I read that in your paper I thought, “Oh my goodness, thatâ€s really interesting that weâ€ve all got it backwards.” But then I quickly rationalized and said, “Well, I guess what I always assumed was that the steepness was on the axis referring to difficulty somehow,” right? And that if a task is particularly difficult, then thatâ€s the steepness, and thatâ€s the curve Iâ€m on. So really, when we encounter something thatâ€s really difficult, and weâ€re having a hard time mastering it, we should say weâ€re on a very shallow —

LILIENFELD: A very shallow learning curve, thatâ€s right. I think when people say, “This task has a steep learning curve,” what they mean is, “Man, I feel like Iâ€m going up like Sisyphus pushing the rock up the hill and going up a very steep mountain!” But in fact if something has a steep learning curve, that means that itâ€s acquired very quickly.

Listen to the episode here.