Hey wait, good point, what the heck kind of data structure even is a stack of papers? You can insert like a linked list but hop around like an array.
Only for reasonably small stacks. Insertions at random indices won't stay O(1) when you're dealing with 100k pages and more – i.e., when you can't pick them up in one movement.
I guess such a stack would fall over quickly, resulting in a heap. But again not the programming one.