In an emotional moment, a character gets someone's name wrong. Often this reveals that current drama has triggered a memory of a similar situation in the past. If the name isn't familiar, cue a Flash Back to who they were; if it is, there's probably some backstory between the characters we weren't aware of before. If the wrong name pops up during sex (or at the altar), the speaker may not live much longer. A You Remind Me of X situation may prompt this. Only counts if it makes it to a final cut, so somebody calling a character by the actor's name in the Blooper Reel isn't one of these.