Our default state of the mind is called mind wandering, where it is incessantly busy thinking about mostly random stuff. We are not even aware of this. But what we know is that wandering mind is not happy mind.
Meditation or the mindful state, breaks the spell of a mind wandering and in breaking the spell of wandering mind, it helps us to come to the realization that, it is possible for us mind to transcend the usual worry state.
Read full article here. Breaking mind-wandering