I also like this idea. At first I thought it was kind of pessimistic, but then I thought about it and really it's not because it's naive to think that you won't have hard times in your marriage.
The tradition goes something like this: The couple writes love letters to each other. In their letters, they detail why they fell in love with each other and what they really, truly admire about the other person. The letters get sealed up before they are read by the person they are intended for.
The sealed letters are brought out at the end of the ceremony. They are put into a wooden box that the couple supplies. Along with their letters, they put a nice bottle of wine into the box with two glasses. Once all is in the box, the wedding party hammers nails into the box to close it.
The point of all this? If, at any point, the marriage is in serious jeopardy, the couple is to open the box, read the letters about why they fell in love with each other in the first place, and drink the wine together before making any irrational decisions.
While, some could see this as a somewhat solemn ritual and not a celebratory or joyous tradition, I see it as being realistic and somewhat romantic. It’s a metaphor for keeping the marriage based in truth and what is real. The hope is that you won’t have to open the box but, who knows, maybe on your 40th anniversary, it’s a treat.