Just as a person who does not know the numbers can’t solve mathematical problems, a person who is incapable of seeing what exists does not understand problems in the world.
Socrates could be one of the four Great Teachers of mankind owing to knowing that he did not properly appreciate what exists in the world. 'Know yourself.' It means you need to know yourself who can't see things as they are. To the people of the world, it is nothing but words. Even though they cannot see things as they are, they say and act under the illusion that they can.