He further argued that , as humans develop , they become fixated on different and specific objects through their stages of development -- first in the oral stage ( exemplified by an infant 's pleasure in nursing ) , then in the anal stage ( exemplified by a toddler 's pleasure in evacuating his or her bowels ) , then in the phallic stage . He further argued that , as humans develop , they become fixated on different and specific objects through their stages of developmentâ '' first in the oral stage ( exemplified by an infant 's pleasure in nursing ) , then in the anal stage ( exemplified by a toddler 's pleasure in evacuating his or her bowels ) , then in the phallic stage .