We all want to believe there's more to life than just the day-to-day grind. For this reason, many characters will embark on the journey to discover their purpose—why they're here, what they personally can do that no one else can, how they can contribute and whose lives they can impact.

Saving someone (from addiction, suicide, poverty, imprisonment, etc.)
Helping a group of people—i.e., Mother Theresa and the people of Calcutta
Bringing a needed innovation to people in need (clean water, medicine, an energy source, etc.)
Financially serving others
Going into ministry as a pastor, nun, missionary, etc.
Caring for someone (such as a child or elderly relative) who can't care for themselves
Fostering or adopting children
Fighting injustice or oppression
Embracing a vocation that enables one to serve others (teaching, running a business so one can employ those who are typically unemployable, etc.)
Opening a business or non-profit meant to help others (providing laundry services to the homeless, caring for abandoned pets, building homes for disabled veterans, etc.)
Opening one's home to those in need
Reuniting loved ones who have been estranged or physically separated
Volunteering in a meaningful way (mentoring young people, making baby blankets, providing free financial advice, etc.)
Bringing the guilty to justice
Using one's giftedness
Bringing joy to others

There are five basic human needs that, when missing from a character's life, could motivate them to pursue this goal. The following needs are all possibilities, but only one of them should be the primary driver for any given character. For more information on the relationship between human needs and outer motivations, please see this Character Motivation tutorial.

Self-Actualization: If the character has a cause that is deeply personal to them and they believe achieving it will give their life deeper meaning or right a wrong, this need would drive them to achieve this goal.
Esteem and Recognition: A character's self-esteem may drive them toward this goal if they've been making the wrong choices and feel badly about them, as in the case of someone pursuing an affluent career, knowing they're denying a calling elsewhere. When their self-esteem hits a critical low, they may embrace change and choose to follow the path they know they're meant to walk.
Love and Belonging: If a character has been isolated or separated emotionally from loved ones, they would know how this feels and want to keep others from suffering through it. This desire may push them to pursue a goal that would help others who are struggling with a lack of love and belonging.