Nope. Just like the MacArthur quote, it is attributed to Plato on a thousand web pages, but apparently incorrectly. There is never a citation, such as a Chapter in The Republic. I just looked on 11 Google pages, and did not find a genuine attribution to Plato, maybe you can find a specific citation, I couldn't.
Apparently according to who? So you have a citation for it from someone else? You may want to forward it to brainyquote.com. They've sure got it attributed to Plato.