"There is only one way to happiness and that is to cease worrying about things which are beyond the power of our will."--Epictetus

Like the past and the future. They are both beyond our ability to change or control.  The past is gone.  The future hasn't happened yet.  Both are outside the workings of our will.
Yet it's so easy to drag the miserable past into a similar present, the ghost of it chilling the heart and destroying our enjoyment of the moment.
Or we worry about what comes next and how this moment might affect our future.
Happiness is a moment to moment thing. Our power, our will, only exists in this moment.
This moment.
Now.
Ignore the past.
Disregard the future.
Choose to be happy now.