Freud's structural model .
The Id is instinctive, impulsive, neotenous. It demands constant satisfaction, craves instant gratification, and has little future time orientation. The Id is impulsive and shallow concerned mostly with sense fulfillment.
The ego is considered to the be intermediary for the id. It rationalizes the ids constant desire for pleasure, it's poor impulse control, and it's constant desire for more. Anyone familiar with the rationalization hamster might think that the two sound similar. Most likely, they are. The hamster is the ego. The ego is the hamster. The hamster is driven by emotions which is driven by base desires. Logic only comes to a factor in rationalizing the impulsive behavior to assuage any uncomfortable feelings of guilt.