A reversal is just anything that's a surprise. It's a way of keeping the audience interested.
“St. Paul's Chapel stands - without so much as a broken window. Little miracle.”
“And they didn't have to get into a lot of legal speak or talk ER terms, they were real people. I think that's why so many actresses were attracted to it. And it was just about problems that you could identify with so much, right off the bat.”