It helps to read this quotation within the context of the entire entry Anne Frank makes on this particular day. She is struggling with the idea that some people do not make the choice to be ethical or moral, saying, "It strikes fear to my heart when Peter talks of later being a criminal, or of gambling..." (254). It concerns her that not everyone will even try to do the right thing, making an excuse of weakness. She goes on to suggest that happiness must be earned, saying, "You must work and do good..." (255). She then goes on to talk about how "upholding one's own honor and conscience...(256). When Frank ends with this quote, what she mean by having a quiet conscience? Someone who has tried every day to do the right thing has a quiet conscience because he or she is not troubled by wrongdoing. That gives a person a source of strength that could not possibly come from having a troubled conscience and an awareness of having not tried to do one's best. Every time I read her diary, it amazes me how wise Anne Frank was, at such a young age, and during such a troubled life.