The eye scans a certain way, and to be honest, I have given up even trying to decipher the how, when and why.
All I know is that it does.
We play with shapes from the earliest age. Blocks, then maybe paper and glue, then looking and daydreaming with no purpose other than to not concentrate on whatever lies inside the periphery, or is it outside? Never mind.
Dancing dust motes are infinitely more interesting when you squint into the bright light.