Sigmund Freud in his psychosexual theory states that there are five stages of development which must be completed successfully for an individual to have a healthy personality. These stages are: oral, anal, phallic, latent and genital during which time a child is presented with conflict emanating from their sexual drive and social expectations. Connected to these stages is the human mind that is divided into three parts: the id, the ego and the superego. These three are in constant conflict with each other throughout the five developmental stages. The id, which is irrational and acts based on the pleasure principle, is regulated by the ego and superego which act on reality and morality principles respectively.
A successful navigation of the stages which involves adequate conflict resolution results in a fully functional mature personality. On the other hand, if an individual displays neuroses, it means that there was unresolved conflict during the developmental stages leading to fixation. For example, an aggressive personality or an overly dependent personality is a result of fixation from the oral stage whereas a personality seeking control or obsessed with organization is a result of fixation from the anal stage of development.