What is "Fei Li Wu Shi"(Don't look at things you shouldn't)?

If you've spent any time in China, or watched some Chinese martial arts stories and films, there's a good chance you've heard a phrase a lot: "Fei Li Wu Shi"(Don't look at things you shouldn't). But what exactly is something you shouldn't look at? This brings us to another of Confucius' ideas: li (Rites).

Confucius considered li to be a general rule, whether in political governance, personal cultivation or family life. Even virtues have to be moderated by rites: being respectful without li would only exhaust people; being cautious without li makes one timid and weak; being courageous without li brings trouble; being honest without li hurts people's feelings through frankness. “Rites” were considered so vital that Confucius demanded that one should never look at, or listen to, or say, or do whatever goes against li.