Researchers have shown that even an individual can produce the wisdom of the crowds, called “the wisdom of the inner crowd.” However, the previous methods leave room for improvements in terms of efficacy and response time. This paper proposes a more efficient method, which required a short time, based on findings from cognitive and social psychology. The procedure is to ask participants to give two answers to the same question: first, their own estimate and, second, their estimate of public opinion. Experiments using this method showed that the averages of the two estimates were more accurate than the participants’ first estimates. That is, the wisdom of the inner crowd elicited. In addition, we found that the method could be superior to other methods in terms of efficacy and convenience. Moreover, we identified the conditions where our method worked better. We further clarify the availability and limitations of using the wisdom of the inner crowd. Overall, this paper proposes an effective and short-time method for harvesting the wisdom of the inner crowd.