As in all sweetest music,

a tinge of sadness was in every note. Nor do we know how much of the pleasures even of life we owe to the intermingled sorrows. Joy cannot unfold the deepest truths, although deepest truth must be deepest joy. Cometh white-robed Sorrow, stooping and wan, and flingeth wide the doors she may not enter. Almost we linger with Sorrow for very love.

Phantastes, chapter X,
George MacDonald