Freud suggested that behaviour is influenced by early childhood experiences and the tripartite personality. Traumatic events (e.g. abuse) are repressed into the unconscious mind and affect personality because it may lead to depression.
This can be seen in Freud's theory as over or under gratification in the 5 stages can lead to a fixation at that stage which is when you become emotionally stuck on a stage.
During the first 3 stages our ego and superego are developed.
In the oral stage we learn to be dependent and to trust other people…