In the case of QM, I think the concrete physical cases are all counter-intuitive. They trigger the wrong ideas and confuse people instead of helping them, e.g.

In the case of QM, I think the concrete physical cases are all counter-intuitive. They trigger the wrong ideas and confuse people instead of helping them, e.g. by having them focus on malformed questions like "is it a particle or is it a wave?". Which is not to say that I think you should do two years of linear algebra before understanding how the heck it applies to reality. That would also be insane. I guess I just think that the first concrete case should be a qubit simulator. Something grounded that you can come back to and say "Well, what if I did this?" and get the right answer.