"We may, indeed, say that the hour of death is uncertain, but..." — Marcel Proust quote meaning

We may, indeed, say that the hour of death is uncertain, but when we say so we represent that hour to ourselves as situated in a vague and remote expanse of time, it never occurs to us that it can have any connexion with the day that has already dawned, or may signify that death — or its first assault and partial possession of us, after which it will never leave hold of us again — may occur this very afternoon, so far from uncertain, this afternoon every hour of which has already been allotted to some occupation. You make a point of taking your drive every day so that in a month’s time you will have had the full benefit of the fresh air; you have hesitated over which cloak you will take, which cabman to call, you are in the cab, the whole day lies before you, short because you have to be at home early, as a friend is coming to see you; you hope that it will be as fine again to-morrow; and you have no suspicion that death, which has been making its way towards you along another plane, shrouded in an impenetrable darkness, has chosen precisely this day of all days to make its appearance, in a few minutes’ time, more or less, at the moment when the carriage has reached the Champs-Elysées.