When the feeling of immortality passes.

It is said that teenagers and younger have a feeling of almost immortality: that the likelyhood of dying is so slim that it gets no thought put to it: Dying is for the old. It is also said that once one becomes an adult one then loses this sense of imortality.

I can attest to that. However I do not think this happens because one "becomes an adult". I think this happens because one of your parents die. The teenage to young adult time is when often a parent will die, otherwise it's when a person is about 30 to 40 (which is cited as another time when someone gains a sense of mortality). When other people die it means usually not that much: they were bit players on the stage of your life. When a parent dies... well that person... that person was 1/3rd of your life. When a parent dies a REAL person dies, not some actor you see once in awhile.

You then realize that you too can die.
And you will die.

Maybe of a heart problem, maybe an auto accident, if you're lucky a muslim terrorist organization will personally saw off your head really really really really mega ultra slowly while filming it in high definition... but you will die.