One criticism that is levied against traditional economic and finance models is that they are often formulated as if the typical decision maker were an individual with unlimited cerebral RAM. Such a decision maker would consider all the relevant information and come up with the best choice. However, we know from this course that normal human beings are imperfect. And the information requirements for these models are totally egregious. Consider CAPM for a moment. This model assumes that investors are capable of studying the universe of securities in order to come up with all required model inputs. These inputs include expected returns and variances for all securities, as well as the co-variances among all securities.

Q.1 Why do people create models that people really cannot follow?

Q.2 Why do people assume people can do all these calculations?

Q. 3 Why does people assume people are so rational?