Heartbeat Retrospectives

I am sometimes asked by people wanting to understand more about retrospectives "Can you tell me a story that demonstrates a powerful outcome that resulted from a retrospective?". Sorry, I am not able to produce a fantastic retrospective story out of a hat. I have come to realize that this question is similar to "Can you tell me about a grand design that resulted from regular refactoring code?" or "Can you tell me about a disease that was cured by taking regular exercise?". These questions make an assumption about the result of a practice and then ask for confirming evidence. The power of regular refactoring, regular retrospectives and regular exercise is that they prevent big problems from happening so there should be no war stories or miraculous transformations! Of course, I have worked with teams where running regular heartbeat retrospectives made a big difference in the long term but because the changes were gradual and slow they don't make great elevator pitches.