Freud is inspiring

I was amazed by how Freud uses the idea of psychoanalysis to try to understand human subjects. What I have never thought about before reading Freud is that humans have different degrees of damages. Freud points out that sexual instinct is present in childhood behaviors such as thumb sucking. If we were to go back to the childhood to find out what is wrong, how could  we define if  the sucking activity is for sexual pleasure? This is a very challenging question to me because I have been told that newborn babies are innocent. However, I am convinced that human is constantly seeking the feeling of satisfaction. It is not that children are exposed to the idea of sexuality as they grow up and mature, but rather they are born with these characters. As Freud argues that psychoanalysis is trying to help rather than trying to fix, I begin to see why he thinks it is critical to study sexual instinct in childhood. The nature of the feeling of pleasure is what driving Freud's argument in sexuality.