now is once is nothing

And again he thought the thought we already know: Human life occurs only once, and the reason we cannot determine which of our decisions are good and which bad is that in a given situation we can only make one decision; we are not granted a second, third, or fourth life in which to compare various decisions.

...

Einmal ist keinmal.What happens but once might as well not have happened at all. The history of the Czechs will not be repeated, nor will the history of Europe. The history of the Czechs and of Europe is a pair of sketches from the pen of mankind's fateful inexperience. History is as light as individual human life, unbearably light, light as a feather, as dust swirling into the air, as whatever will no longer exist tomorrow.

-- Milan Kundera, The Unbearable Lightness of Being (translated from Czech by Michael Henry Heim)