||Contrary to early workings assuming rationality to passively ‘be given', increased attention on the nature of rationality has brought its role as an assumption into question. Through the framework of Portfolio Theory, a practice dictating the management and allocation of financial assets subject to risk and return, this paper seeks to examine rationality as it pertains to the crossover between theory and empiricism. Analysis shall encompass both theoretical and epistemological critiques. Additionally, this paper maintains that behavioral facets act as mental restrictions inhibiting rational decisions. Ultimately, this paper argues Portfolio Theory assumes, but does not exemplify, rationality in the conventional (orthodox) sense. Pursuant to a neoclassical (mainstream) perspective of individuals comprising society, insofar as irrationality continues to prevail within the individual, this project asserts, so too shall it continue to prevail in the markets of individuals.