I always go back to this strip by Bill Watterson's
Calvin and Hobbes. This was the strip that ran when the series ended many years ago. While it feels quite precious in the exchange between the two, the far more endearing aspect of this strip is its optimisim—and this is what everyone should have every single day of their lives. (In fact, my General Psychology final project ended with this same strip as a metaphor to how my life in college—essentially, my schooling life—is going to end with me looking forward to even greater and brighter things. And this, despite the fact I won't have the comfort—or safety blanket—of a new semester once summer was over.)
Look forward to the day being fantastic, look forward to great things, look forward to learning something new everyday. If the day turned out to be a dud, then there's always the next day to make things better. Once you lose this enthusiasm, well, you've lost the battle of life.