The present moment

"Remember that man lives only in the present, in this fleeting instant: all the rest of his life is either past and gone, or not yet revealed."

"Were you to live three thousand years, or even thirty thousand, remember that the sole life which a man can lose is that which he is living at the moment; and furthermore, that he can have no other life except the one he loses. This means that the longest life and the shortest amount to the same thing. For the passing minute is every man's equal possession, but what has once gone by is not ours. Our loss, therefore, is limited to that one fleeting instant, since no one can lose what is already past, nor yet what is still to come -- for how can he be deprived of what he does not possess?"

"To live each day as though one's last, never flustered, never apathetic, never attitudinizing -- here is the perfection of character."

- Marcus Aurelius

"There is surely nothing other than the single purpose of the present moment. A man's whole life is a succession of moment after moment. If one fully understands the present moment, there will be nothing else to do, and nothing else to pursue. Live being true to the single purpose of the moment."
- Hagakure