Do not dwell in the past, do not dwell in the future, concentrate the mind on the present moment.
There is neither past nor future. There is only the present. Yesterday was the present to you when you experienced it, and tomorrow will be also the present when you experience it.
We should not fret for what is past, nor should we be anxious about the future; men of discernment deal only with the present moment.
We are responsible for what we are, and whatever we wish ourselves to be, we have the power to make ourselves. If what we are now has been the result of our own past actions, it certainly follows that whatever we wish to be in future can be produced by our present actions; so we have to know how to act.
You must live in the present, launch yourself on every wave, find your eternity in each moment.
Henry D Thoreau