>It's the computer equivalent of decorating a room - "I think the couch would look great against that wall", you move couch, "Nope, I don't like it there."
>
>Basically it thinks the index will help based on the query analysis it does, but once you create it (and it can actually use it for analysis), it decides some other option is better.

Yes, and this is highly complicated. We have no guarantee that the requested index serves for something. And, because the visual does not show it, we cannot no if with one million more records, it would still use it.