Why is the ring of vertices not complete? I'm a beginner at blender and I'm trying to make a donut with icing with this tutorial: https://www.youtube.com/watch?v=f5Gb1VK98Wc&amp;t=456s . At 33:30 He shows how to make a curvy edge to the icing, but I can't seem to make it work. He shows how to hide the top of the icing so you end up with one outer and one inner ring of vertices. But when I do this my outer ring is not complete. It's missing one line between two vertices. Should I just simply add a line between these two? And if so, how? Anyone who can tell what I've done wrong?
I think I know what you did. You had a vert or an edge of the line selected and then added the stuff you wanted to hide with box select. The previous selected vert or edge was also still selected.

You could have hit A to deselect it before the box select.

What you just need to do now is press Alt-H to unhide everything (or Mesh -> Show/Hide -> Show hidden), do your selection again and hide it again.