When taking a live photo, your iPhone automatically chooses a keyframe to serve as a n-animated thumbnail. Depending your subject, this automatic choice can be terrible, showing a fuzzy frame, or worse. If you took a picture of a skater doing a slap heel, for example, it may be that the frame does not even have the skater.
The good news is that you can easily choose your own keyframe.
How to choose a keyframe for your live photos