Late last month, Robert Shiller stopped by Motley Fool Headquarters for an hour-long interview about housing, stocks, bubbles, and more. A Yale professor who just published his 10th book, Finance and the Good Society, Shiller is an expert on a variety of economic topics.

Given his clout within the field, I asked him about the biggest change in his investment thinking over his long career (he's been a professor at Yale since the early 1980s).

In the video below, see why he thinks the efficient markets hypothesis is a "half-truth," and see what he thinks is really driving the markets these days. (Run time is 2:19; a transcript is below.)