Understanding the Millie Mind

Millie, can you please explain to me why you do figure eights in the backyard, repeatedly sniffing the same four places before deciding on the perfect spot to use the bathroom? I know this is not a unique trait. I know many, if not most, dogs do this. But I don’t understand.
Why was that one spot on the grass unacceptable on the first few sniffs, only to suddenly be the one acceptable place for your “business?” Could you imagine if humans did that? Constantly running between restrooms before finally deciding on the perfect one? Looking into a stall, looking into the next one, then looking into the first one again?
It’s just another Millie mystery.