Holy cow, I wrote a book!
When you view a folder for the first time,
Explorer arranges the items in a nice default pattern.
And when items are added to the folder,
they get added to the end.
And when you delete an item from the folder...
the other items auto-arrange to close the gap?
But wait, if you look at the View options,
the Auto-Arrange option is not set.
So are we auto-arranging or not auto-arranging?
Well, yes, but only until you touch it.
As long as you express no interest in the placement of icons
in a folder (and the desktop counts as a folder),
then Explorer will auto-arrange them.
But once you move an icon around,
Explorer will turn off its double secret auto-arrangement
and leave the icon arrangement to you.
this mode is known as