1) Nobody else has ever thought of your question, even though all of the pieces of knowledge needed to formulate it have been known for years. If the field has many people involved, the probability of this is vanishingly small and you should systematically disabuse yourself of your fantasies if you think like this often.

I think this might underestimate the number of good questions/ideas in a field relative to the number of researchers. I think humans are already dealing with utterly huge problem spaces and carving out little areas of working technology, But there are many orders of magnitude times more of other possible technologies.

It could be that your idea is based on old information, but you only thought of it because it serves some weird specific goal, and no one in history has had that goal and knowledge of your field.

Or you're combining old information from several obscure fields.

I think there are other hints as to whether your ideas has been though of before, but I don't have a way to express them other than "obviousness".