Quiz

If the polygon is not flat, then the intersection of all its sides is impossible, because a straight line intersecting two of its sides lies entirely in the plane of those sides and cannot intersect sides lying in other planes.

Well, it just won't work. I would say it like this: if you build two connected segments and intersect them with a straight line, then the next segment, connected to the previous one and intersecting the same straight line, lies in the same plane. Repeat n times.