"If it is not right do not do it; if it is not true, do not say it." -Marcus Aurelius 

What this quote is saying is that if you no that the action you are going to take is wrong then do not do it. If you are going to say something or spread rumors about something/someone that isn't true then don't say it. Basically it means to not do things that aren't right. An example is that if someone ask's you to say something that isn't true be brave enough to say no.