But otherwise, I have to disagree. Electromagnetism is perfectly comprehensible, since you can visualize it (comparatively) easily and relate it to the everyday life. And usage of QM? I mean — any smartphone or computer today uses tons of miniaturized components that we could make only because we know QM well. Without understanding QM, we would still be in the age of computers taking up a whole building. Due to the immense computer and smartphone boom, QM, although weird, is probably the best-tested physical theory ever, and the one that is maybe most practically used as well.