What does this quote mean? "Character is what you are in the dark." - Dwight Lyman Moody

Character is defined as "the mental and moral qualities distinctive to an individual". This quote is suggesting that your true character is shown when you aren't around other people; when you're alone (hence "in the dark"; no one can see you wen you're alone). Peer pressure might cause you to hide you true feelings or conform to what others are thinking, when you're with other people.

I personally think this means the way you deal with things during a dark time shows a lot about your character and self.