All the assumptions that make a database index work will break. If you think about any kind of binary tree based structure, it will have invariants like "the l

All the assumptions that make a database index work will break. If you think about any kind of binary tree based structure, it will have invariants like "the left child node will be less than the parent node, and the right child node will be greater than the parent node." If those are violated just a little bit, at best data will simply disappear from the index. It's possible for updates to delete stuff, or for operations on the index to hang.