I am trying to animate a hinged lid so that the hinge will not poke through the bottom, and that it will also properly show itself. I followed many tutorials word-for-word, but when I do what they do, the animation doesn't play properly. I added a keyframe to the hinge called "Stretched", and then edited it by stretching part of it. It checks out, because when I click the pin after clicking "stretched", the object morphs instantly to the stretched shape key. However, when I set the slider to 0 and create a keyframe at frame 0, then set the slider to 1 and create a keyframe at frame 70 (end of animation), nothing happens. The hinge doesn't stretch. I've made sure to turn off all pins and such, but nothing helps. Here are pics:
In your screenshot you can see that your "stretched" shape key was relative to the "stretched" shape key instead of the Basis shape key. Since it was relative to itself, it represented no deltas. If you change "stretched"'s Blend: relative_key from "stretched" to "Basis", then the shape key works.