Quantum mechanics

The maths and ideas used in deriving quantum mechanics are very complicated, but many conclusions reached from it are very understandable and practically useful.

This means that students are first taught quantum-mechanical conclusions long before the ability to work them out for ourselves, if we ever do. For training a practical chemist, that's a good idea. For some students that can be unsatisfying.

Vocabulary can sometimes mask our ignorance. "orbital angular momentum quantum number" sounds a lot more clever then "mysterious number which partly describes an atom, which follows slightly different rules to the other numbers".

But the second quote more accurately describes what the number means to people learning the conclusions first. Of all the people who use quantum mechanical vocabulary, few do it with confidence.