According to Markowitz, an investment in risky security is presumed to select an investment portfolio which is on the EFFICIENT FRONTIER and tangent on the investor indifference curve. However, in practice neither the efficient frontier nor the INDIFFERENCE CURVE can be estimated with high degree of accuracy. Therefore, the PORTFOLIO THEORY may be redundant. Explain the term in in capital letters in the above statement and critically asses their validity with reference to be above theoretical argument.