I think of it in terms of degrees of freedom and statistical likelihood. If I throw a bunch of marbles on the floor and a few of them form a interesting shape

I think of it in terms of degrees of freedom and statistical likelihood. If I throw a bunch of marbles on the floor and a few of them form a interesting shape that is one thing as they can only move on a plane. If I throw them in the air it is less likely to form a circle as now they are free to move in multiple directions and are not constrained to the plane. If 4 of those marbles align that is less likely than 20 of them happening to do so in a recognizable shape. 20 marbles in the air, each one being in just the right place relative to the 19 others in order to look like a circle when they can be in any position in space (vs. limited to a flat plane) is exceedingly unlikely. Even more unlikely is that an arc appears next to the ring, that would make me start to wonder if something is affecting the marbles I throw into the sky.