According to Markowitz, an investment in risky security is presumed to select an investment portfolio which is on theefficient frontierand tangent on the investorindifference curve. However, in practice neither the efficient frontier nor the indifference curve can be estimated with high degree of accuracy. Therefore, theportfolio theorymay be redundant. Explain the terms in bold in the above statement and critically assess their validity with reference to the above theoretical argument.