Hagakure

"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.
Everyone lets the present moment slip by, then looks for it as though he thought it were somewhere else. No one seems to have noticed this fact. But grasping this firmly, one must pile experience upon experience. And once one has come to this understanding he will be a different person from that point on, though he may not always bear it in mind.
When one understands this settling into single-mindedness well, his affairs will thin out. Loyalty is also contained within this single-mindedness."
- From the 2nd Chapter, Hagakure, Yamamoto Tsunetomo