For simplicity: a sphere. No angles to count or measure degrees of, no corners to snag a hem on, just center-point, radii, surface, volume. Subtract one dimension and you have a circle — center, radius, circumference. Both forms roll. Polygons will roll erratically then come to rest on one side. A true sphere could roll on an infinite plane for an eternity.
Fortunately we’ve evolved to live in a finite world filled with lumps and imperfections. Approximately spherical is usually good enough for us and it’s Mother Nature’s way. The following are examples of groups of spheres because it was the natural groupings that first caught my eye.
Fields of Rounds is the Pinterest board that I swept the groupings into. You’ll see that I’ve added human images but that’s for another day. Spheres and Circularity may interest you too.
Remember, if you’d like to argue that circles aren’t so simplex all you have to say is pi.