"he theories proposed by Sigmund Freud stressed the importance of childhood events and experiences, but almost exclusively focused on mental disorders rather that normal functioning.  According to Freud, child development is described as a series of 'psychosexual stages.' In ""Three Essays on Sexuality"" (1915), Freud outlined these stages as oral, anal, phallic, latency and genital. Each stage involves the satisfaction of a libidinal desire and can later play a role in adult personality."
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