With this simple but poignant observation, science-fiction writer Margaret Wander Bonanno — best known for writing a series of "Star Trek" novels between 1985 and 2010 —  muses that life is not an abstract concept, but the aggregate of how we spend each of our days. It’s a surprisingly powerful motivator, a reminder not to waste any time. If we can live in the moment and find gratitude and joy in the present, we will eventually be able to look back on a lifetime of happiness.