Part of every misery is, so to speak, the misery's shadow or reflection: the fact that you don't merely suffer but have to keep on thinking about the fact that you suffer. I not only live each endless day in grief, but live each day thinking about living each day in grief.
It's always winter but it's never Christmas.
My own idea, for what it is worth, is that all sadness which is not either arising from the repentance of a concrete sin and hastening towards concrete amendment or restitution, or else arising from pity and hastening to active assistance, is simply bad; and I think we all sin by needlessly disobeying the apostolic injunction to 'rejoice' as much as by anything else. Humility, after the first shock, is a cheerful virtue.