The saying "Know thyself" may refer by extension to the ideal of understanding human behavior, morals, and thought, because ultimately to understand oneself is to understand other humans as well. However, the ancient Greek philosophers thought that no man can ever comprehend the human spirit and thought thoroughly, so it would have been almost inconceivable to know oneself fully. Therefore, the saying may refer to a less ambitious ideal, such as knowing one's own habits, morals, temperament, ability to control anger, and other aspects of human behavior that we struggle with on a daily basis.
It may also have a mystical interpretation. 'Thyself', is not meant in reference to the egotist, but the ego within self, the I AM consciousness.
Delphi became the site of a major temple to Phoebus Apollo, as well as the Pythian Games and the famous prehistoric oracle. Even in Roman times, hundreds of votive statues remained, described by Pliny the Younger and seen by Pausanias. Supposedly carved into the temple were three phrases: γνωθι σεαυτόν (gnothi seauton = "know thyself") and μηδέν άγαν (meden agan = "nothing in excess"), and Εγγύα πάρα δ'ατη (eggua para d'atē = "make a pledge and mischief is nigh"), as well as a large letter E. Among other things epsilon signifies the number 5. Plutarch's essay on the meaning of the “E at Delphi" is the only literary source for the inscription. In ancient times, the origin of these phrases was attributed to one or more of the Seven Sages of Greece, though ancient as well as modern scholars have doubted the legitimacy of such ascriptions. According to one pair of scholars, "The actual authorship of the three maxims set up on the Delphian temple may be left uncertain. Most likely they were popular proverbs, which tended later to be attributed to particular sages
"Let no one destitute of geometry enter my doors." Plato (c. 427 - 347 B.C.E.)
"[Geometry is] . . . persued for the sake of the knowledge of what eternally exists, and not of what comes for a moment into existence, and then perishes, ...[it] must draw the soul towards truth and give the finishing touch to the philosophic spirit."