> Once again, we don’t have a satisfying explanation why. We know that these quantum numbers correspond to standing-wave solutions of a three-dimensional wave function that we pulled out of thin air. We also know that the model works better than any alternatives. But we don’t know what any of it really means — or if it means anything.

It is so refreshing to see this explicated thus; physics textbooks are generally coy about "know this for now, and there will be deeper insights available later" but they typically never level with readers and say "we don't know".