I would say that it's not so much about exchanging seeking of your happiness for seeking happiness for others. After all, seeking happiness for others can very quickly turn into another quest for glory. Just look at all those proud charitable folks always eager to impose their help on other people and getting kicks from it in the process. Thus, the way to humility is more about willingly putting oneself in a subservient position in order to curb one's self-importance.

You will find it in Eastern (but also Judaic and basically any valid) traditions where an apprentice enters into complete surrender to the teacher who then puts the ego of the student through the wringer. You will also find a similar concept in writings of Castaneda where apprentices willingly sought out and entered into subservient relationships with abusive people in position of power, so-called petty tyrants, exactly in order to make themselves empty of themselves. To crush their self-importance.

Because only when one is not full of oneself the Truth can enter, or better said, become apparent. And the final happiness is then merely a byproduct of knowing the Truth.