I watched an old series a long time ago, and one particular scene always stuck with me.

A woman gave a speech, and in it she explained how her language does not have a word for "goodbye".  Instead, her people, in parting, use the expression "until next we meet".  Because, even if it's the last time they will ever be with that person, they look forward to seeing them, perhaps in the afterlife.

I don't know why, but since then I've always made it a point to never say goodbye.