This is a pet peeve of mine so I hope you'll forgive this rant. I found the following image in my G+ stream, and was digesting the quote and noticed it was attributed to Plato. I subscribe to the idea that quotations should be properly sourced, and there wasn't any mention of what book this was from which of course spurred me on to investigate. It's become common to attribute all kinds of new agey quotations to great historical figures on the internet, and while you might like the sentiment, Plato almost certainly would not have. I'm no fan of Plato myself, but while "Wordsworth Dictionary of Musical Quotations" attributes the quote to him, they curiously don't provide a source. There are several folks who have taken the time to point out the problem with this quotation, this one describes the problem with it nicely.
...and I agree with the author here who says: "If you don’t do the work necessary to confirm the source, what you post is no better than chain mail and spam. And the gods know we have enough of that online already."