So many unnecessary heart afflictions, I encounter, because of wandering mind. Either dwelling on the past, wishing I had taken different course of action, or projecting into the future, dreading some imagined outcome. The Buddha is clear on that one:
Let not a person revive the past
Or on the future build his hopes;
For the past has been left behind
And the future has not been reached.
Instead with insight let him see
Each presently arisen state;
Let him know that and be sure of it,
Today the effort must be made;
Tomorrow Death may come, who knows?
No bargain with Mortality
Can keep him and his hordes away,
but one who dwells thus ardently,
Relentlessly, by day, by night -
It is he, the Peaceful Sage has said,
Who has had a single excellent night.
- from Bhaddekaratta Sutta: A Single Excellent Night -
Taming wandering mind, and bringing it back, over and over again, to the present moment. Using the breath, and the power of mindfulness, and concentration, as anchors. All with great patience, and kindness.