Invoked: Alice and Bob reach a milestone (such as their 50th wedding anniversary) that they want to share. For example, during the champagne toast.
Defied: Alice and Bob don't want to bore everyone at their party to death, so rather than expounding on every event from the day they met to the present, they just casually mention a few great moments in their speech and let everyone's memory fill in the rest.
Discussed: "I've put together some clips of our home movies that will show what we've been up to these last few years. Anyone got popcorn?"