Sigmund Freud believed that personality develops through 5 stages of psychosexual development: 1) Oral stage (birth to 1 year) focused on the mouth, which can lead to fixation issues like smoking or nail biting if unresolved 2) Anal stage (1 to 3 years) focused on toilet training and control of bladder/bowels, which can lead to messy or obsessive personalities if mishandled 3) Phallic stage (3 to 6 years) focused on genitals and developing gender identities, which can lead to sexual deviancy or confusion if fixated 4) Latency stage (6 years to puberty) is inactive sexually and focused on skills development to build social skills and confidence