... to get out of bed in the morning? or
...to go to work each day? or
...just to keep going on?

I know that for some people it's dedication to someone/something, for others it's hope for better days and yet for others its doing something they love.
Psychologist Mihaly Czikszentmihalyi talks about what makes life worth living. He describes the secret ingredient of happiness as being 'in flow'. According to his theory, being in flow has seven key aspects. (they are presented around the 14 minute mark)
1. being involved in what we do
2. having a sense of ecstasy
3. inner clarity
4. knowing that what we are trying to do is doable
5. having a sense of serenity
6. timelessness
7. intrinsic motivation

Mihaly Csikszentmihalyi: Flow, the secret to happiness - YouTube