By means of background, the 'safe' flying is when the wing has a perfect arc shape. Most deviations from the arc shape are considered dangerous,
especially when they are unintentional. This photo is a collage of flyers purposefully inducing such tricky situations as part of training.
It may not look too scary here, but when you are sitting in a harness several hundred meters above the ground and half of your wing collapses, the perception changes a lot... :)