The way people write and what they write about can give you a lot of information about the person. Let's say you were reading a story about someone giving a speech, if they say they were feeling nervous or a bit scared to talk in front of all of those people you can conclude that they don't normally like to talk in frog of big crowds and there are going out of their comfort zone to give the speech. When they talk about what they did to calm down and how well the speech did or even what the speech was about you can learn what type of person they are and what they value.