Letters 99.24

Indeed, to forget the beloved dead, to bury their memory along with their bodies, to bewail them bounteously and afterwards think of them but scantily—this is the mark of a soul below that of man. For that is the way in which birds and beasts love their young; their affection is quickly roused and almost reaches madness, but it cools away entirely when its object dies. This quality does not befit a man of sense; he should continue to remember, but should cease to mourn.

Seneca, Letters to Lucilius 99.24, translated by Richard Mott Gummere