If the person merging late had to stop, then it means they went too far without getting a space (because they didn't take the chance they were given or no one g

If the person merging late had to stop, then it means they went too far without getting a space (because they didn't take the chance they were given or no one gave them space). This is the problem with zipper merging: if everyone gets it right it's beautiful but the failure mode is near catastrophic (effectively stopping one lane) and easy to get into. One or two bad actors can ruin it.