There are many slogans of wisdom to learn from - but in my opinion they are a sort of useless, because those who would benefit the most from them are lacking willingness to implement them in their lives.
From my modest observation there is a major resistance to change in people, and even when they intellectually agree with an advice - and Socrates' saying is formed as one - they lack flexibility of an open mind that would allow them to examine their ways with an intention to change something there.
There are too many smart asses around that have an answer to everything, and it's futile to challenge them to give an honest assessment of their life. I have witnessed that time and time again, and Socrates must have as well - those who understand the depth of his words usually don't need them except for an additional inspiration, and those who need them couldn't care less.
And THAT'S why the world is in this mess as we see it - there is no lack of available wisdom, but a lack of willingness to make a use of it.