The only thing common with all people is they all know about their true nature.....I believe somewhere we all have that kind of dark feelings, which we don't show but deep down we all are criminals. We all have our true sides which you don't even realise. Some people think they know very well about each other when they are in a relationship, but my friend you really don't know what other person is thinking about you.
Our brain chemistry is designed in such a way there are thousands of chemical reaction going on and a lot of past memories which is stored deep inside our neurons. Which mix with the godamn reactions and represent our true nature...Believe me, if you are going through tough times, most of the emotions are dark even if we try to fill light in that emotion. We know how long will that light last.