Final answer:
Freud believed that fixation in the phallic stage of psychosexual development can lead to immaturity and an inability to form fulfilling relationships as an adult.
Step-by-step explanation:
Freud believed that it was possible for children to become fixated or "stuck" in the phallic stage of psychosexual development. Fixation at this stage can result in immaturity and an inability to form fulfilling relationships as an adult. The phallic stage occurs from ages 3 to 6 and is characterized by a child's awareness of their body and recognition of differences between boys and girls. During this stage, conflict arises when a child feels a desire for the opposite-sex parent and jealousy towards the same-sex parent.