To be properly aware of your finitude—to realise that death happens to you, that it must happen, and may happen at any moment—is to realise that you do not have time to explore all the multiplicity of options which life places before you. What one is compelled to do, therefore, is to determine which life-options are the important, ‘essential’ ones and which are the trivial distractions, the ‘accidental’ time-wasters which life thrusts one’s way.
Grasping one’s finitude is more than simply realising that there is no time to lose. To be able to make the distinction between essential and irrelevant life-options one must, says Heidegger, grasp one’s life as a ‘totality’, as a ‘whole’. But to do that one must ‘anticipate’ one’s death, ‘run forward’, in imagination, to life’s end. Only by positioning oneself at the end of life and grasping it as if it were completed and past, can one grasp it as a whole.