A victory’s anniversary and a defeat’s anniversary can be the same morning.

The same date carries opposite meanings depending on which side of it you stand on. A parade in one place is a mourning in another, and both are accurate accounts of what happened that morning. Commemoration necessarily takes a position, and it usually does not announce that it has taken one, which is how a single event ends up with two entirely sincere annual observances.

When you mark something, it costs little to know what the same day means elsewhere. That knowledge does not require you to celebrate less, only to stop assuming the meaning is universal. The same applies to family and personal anniversaries, which often carry two versions at the same table.