You don't have to run. Play tennis, cross-country ski, meet a friend for racquetball during your lunch hour. Find a way to work your body hard on a consistent basis and don't decide if you're an optimist or a pessimist until that's the routine. You may not believe how much your outlook on life changes.
When routine, whether in action or attitude, becomes too comfortable or constrictive, it's often a clue we're limiting ourselves. There's an invitation waiting -- to look again and discover a new spaciousness. It's here, in this spaciousness, that we're better able to notice the big things and the little things.