The economic problems in a market economy are so complex that it is very difficult to understand how they work. Economic theories which have developed since Adam Smith published The Wealth of Nations in 1776 help to understand correctly economic situations, but do not guarantee fully the correct understanding of the general public. This paper traces down three factors which bring about fallacies in the general cognition of economic problems, namely ignorance, interest, and instinct. Especially, this paper argues that instincts which have been formed by communal living of mankind for a long time affect much on human judgement on economic problems.