You were born only once but every year you have a birthday. Equally, you will die only once but every year you have a death day, the date on which you will die. It is just that you don't know what it is.
Suppose you could know the date of your death but not the year. Suppose that date is 16 October. Then on that date you would be a little worried and especially careful, both physically and morally. And then on the 17th you could relax for a whole year.