Epicurus, Letter to Menoeceus

Accustom yourself to the belief that death is of no concern to us, since all good and evil lie in sensation and sensation ends with death. Therefore the true belief that death is nothing to us makes a mortal life happy, not by adding to it an infinite time, but by taking away the desire for immortality. For there is no reason why the man who is thoroughly assured that there is nothing to fear in death should find anything to fear in life. So, too, he is foolish who says that he fears death, not because it will be painful when it comes, but because the anticipation of it is painful; for that which is no burden when it is present gives pain to no purpose when it is anticipated. Death, the most dreaded of evils, is therefore of no concern to us; for while we exist death is not present, and when death is present we no longer exist. It is therefore nothing either to the living or to the dead since it is not present to the living, and the dead no longer are.