"jAmbu" is very right in what they tell you.
I would like to add that the tradition of the Bodhisattva in the Mahayana traditions, includes a vow to keep on returning, even after gaining enlightenment and no longer being bound to the cycle of rebirth.
Why? In order to help all other sentient beings attain enlightenment.
And to continue being reborn until ALL sentient beings have attained enlightenment.
Thus, part of the daily practice of Mahayana Buddhism is the repetition of our commitment to attain enlightenment not for ourselves, but for the benefit of all others.
In Tibetan Buddhism, which is my training and also one of the Mahayana traditions, we are taught that two things are required for enlightenment: (1) wisdom (acquired through meditation), and (2) compassion (acquired through the compassion practices ... and definitely bringing out a reduction in our self-centeredness).
Of course, now, we DO have our selfish motivations. We are not enlightened, so this of course we are self-centered.
Psychologically speaking, the more you set these imprints of unselfishness, the more this attitude seeps into you. It helps you become less self-centered. Which is (from the standpoint of psychology) a positive condition: the more self-centered a person is, the more neurotic and unhappy they are.