Every act happens once. This one, now, the reading of this line, is not a rehearsal of an earlier one and will not be repeated by a later one. It happens, it completes, and what completes does not come back.
That sounds like a sad fact and it is not one. It is the reason there is anything new. A happening that could recur exactly would add nothing to the world the second time; whatever genuinely cannot end also cannot begin. The once is what makes arrival possible, and the price of arrival is that nothing is kept.
Notice what the once does not need. It does not need a line. There is no timeline along which acts are arranged such that they cannot be walked back; there is only the plain fact that nothing un-conditions what conditioned it. What you inherited, you cannot un-inherit. What arose on something cannot become that thing’s ancestor. Those are one-way facts, everywhere, and none of them is a direction on a map. “Before” is ancestry, not an address.
The word is doing something unusual, and it is worth pausing on. Almost every word this work leans on can be misread as naming a thing. Once cannot. It is a when, not a what. There is no once sitting somewhere waiting to be had, no once outside the happening it is the happening of. Of all the words available, it is the one that will not let you forget that what is being talked about is an act and not an object.
At the edge of each completing there is something that was not there before, and could not have been read off from what came before it. Not a surprise in the sense of a thing we failed to predict, but genuine arrival: the unprecedented, at the ordinary scale of every ending. This is why the once is not only a limit. It is where the new comes from.
Which is also where this touches a life. Everything you love is finite in exactly this way, and the finitude is not a flaw in it. It is the condition of its being anything at all. What can be lost is what can be had. Every tending is of something that ends, including yours, and the ending is not the enemy of the tending. It is what makes the tending matter.
And the fact that this is stated from inside a life that will also end is not a weakness in the statement. It is the only place anyone has ever stated anything from.