The safest way to make me cry is to sing or play Silent Night.
Since I have read so much cognitive science recently I know how it works. Our memories are stored somewhere in ours brain, in fragments, all mixed up. Somewhere in my brain there is a memory of me sitting under a Christmas tree and listening to a bunch of elderly aunts and uncles singing Silent Night in German, which I sort of understood, but not quite, so it sounded like a magical incantation (which it is in a way). If I just think back about it, I remember it clearly and rationally, and I can state that all these uncles and aunts are dead, which is sad, but inevitable. This won't make me cry. But if I hear Silent Night, even played in a department store, the sound of it evokes the emotional memory: exactly how it felt to be a small child under a tree covered with real candles, the smell of honey buns, anticipation of presents hiding behind the tree. The brain says: this is something lost forever,it triggers a complex chemical process which makes me cry.
On the other hand, someone has said: you can only own forever something that is lost.