Let us see to it that the recollection of those we have lost becomes a pleasure to us. Nobody really cares to cast his mind back to something which he is never going to think of without pain. Inevitable as it is that the names of persons who were dear to us and are now lost should cause us a gnawing sort of pain when we think of them, that pain is not without a pleasure of its own.
Thinking of departed friends is to me something sweet and mellow. For when I had them with me it was with the feeling that I was going to lose them, and now that I have lost them I keep the feeling that I have them with me still.
Seneca, Letters from a Stoic, LETTER LXIII