“Know Thyself” was the inscription in the temple of Apollo at Delphi. However, its meaning may have been quite different from today's understanding of the phrase. We live in a world where individualism and self-assertion and -expression are inbuilt mechanisms and have become the lens through which we see and understand the world.
It seems we are breastfed this kind of knowledge, and it is reinforced and emphasized during the school years and through the mass media of television and the movie industry. It may not be so in various other collectivist cultures and traditions, often collectively referred to as the “East”, but through globalization and the popular entertainment industry, this information or paradigm has been seeping through and influencing other cultures to a strong degree.
If we put the meaning of “Know Thyself” into the Greek conception of humanity and the world, we will realize that they understood this in quite a different manner. Whether the Greeks actually believed in the mythical gods is not always clear, but they perceived a much closer tie of the individual with the family and community.
When Socrates was asked to choose between death or exile, he immediately chose the former as exile would have brought unspeakable suffering to one who strongly identifies himself with his culture and people. In fact, the modern notion of individuality did not exist until after the Renaissance and for an ancient Greek, each person was intricately defined through one's nation, family, and status. Each of those terms, with the inclusion of fate and destiny, are but extensions or the extremities of the individual body. One could not exist apart from the other.
“Know Thyself” would mean something like “know thy limits and limitations.” Humans ought to temper their inflated pride and not be blinded by arrogance and vanity but should find their humble nest in the complex harmonious order and unity that exists in the universe, a universe driven by forces unknown and unintelligible to the human mind.
Of course, one could also argue with a mystic understanding of the term, the realization that the self cannot exist apart from everyone else, that all is a reflection of the divine that exists in equal measure in all living - and perhaps even non-living things - as is the case with the philosophies of Neo-Platonism as well as Hinduism.
This idea of the dangers of knowing too much and of drawing limits to human ambition has also been expressed in the famous work of Frankenstein by Mary Shelley. There a curious and highly ambitious scientist wants to play God and creates life. This experiment, however, has drastic consequences for him and others and completely ruins him and his family. As a result, he warns others of avoiding the same kind of mistakes he has made.
This was an interesting message in a romantic climate where most poets and writers were pursuing the higher and occult arts to attain ultimate godlike knowledge. Yet the voice of Mary Shelley is one of caution and of knowing where one's limits lie, just like the inscription at the Delphi.