Our minds are constantly filled with narratives of our own creation. These narratives define who we are, and who we are conditions the narratives. When our outlook is bleak, the narrative becomes bleak, which only darkens our outlook. This negative cycle can continue in a downward spiral with tragic consequences, such as in the case of young Amanda Todd.
Alternately, a positive outlook creates a happier narrative, which accentuates the positive and improves our outlook. While this is a happier occurrence, reality isn't always seen through "rose-colored glasses" and we can find ourselves blindsided when fate suddenly taps us on the shoulder.
Meditation is a way to break these cycles. Sitting still and quieting the mind, we can stop listening to the narration (even if the narrative itself never really quite stops). In deep states of meditation, body and mind drop away, and when there is no narration, there is no narrator.
When the bell rings and we come back to the world, we have a chance, if even for a minute, to see things as they are outside of the influence of the outlook-narrative cycles. Eventually, habitual tendencies of the mind will reestablish themselves, but we can always return to our meditation practice before they become too deeply entrenched. With time, we learn to not get as caught up in them as we had before our practice began.