Music Monday: the saddest Christmas song ever

I love this melancholy, beautiful song from the 1940s musical Meet Me In St Louis.  And ok, so it might not be the saddest but it's certainly one of the most bittersweet in the Christmas canon.  If I knew lots about music I could probably point out that it sounds sad because of a descending minor chord progression in the chorus or something, but I don't so I won't.  For me, it's all about Garland's delivery; the way she makes the line "let your heart be light" sound anything but light and cheerful.  Today I'm feeling exhausted, headachey, sick of children and horrified that we still have another three days of school to get through, so melancholy suits me down to the ground.