Either case can result in great and unnecessary expenditure of emotional and financial energy. Everyone's OK right now. The simplest answer to this is that if you need it suddenly, it may then be too late to get it. Putting this off doesn't make it go away . I don't like to deal with lawyers unless I have to.
Preparation is a positive legal interaction.
Reactive situations often involve negative elements. My relative doesn't understand finances. All the more reason to get such documents in place. Or you can wait to discover that Aunt Sally hasn't paid income taxes for the last four years because she thought that once you were over eighty you didn't have to pay anymore. Today's not a good time to talk about this.