Letters 63.12

What I am about to add is, I know, a very hackneyed remark, but I shall not omit it simply because it is a common phrase: A man ends his grief by the mere passing of time, even if he has not ended it of his own accord. But the most shameful cure for sorrow, in the case of a sensible man, is to grow weary of sorrowing. I should prefer you to abandon grief, rather than have grief abandon you; and you should stop grieving as soon as possible, since, even if you wish to do so, it is impossible to keep it up for a long time.

Seneca, Letters to Lucilius 63.12, translated by Richard Mott Gummere