Great point. The maxim loses some of its utility in the deepest depths of science, although perhaps that will change at some point in the future. Scientific theory is constantly evolving, and there may come a day when clean, ordinary explanations for quantum entanglement, dark matter, and black hole boundaries are available. Or not. But the concept of ordinary explanations a is worth keeping in mind even if there are exceptions. Day-to-day life is pretty ordinary.

It’s worth noting that this was back before astrophysics had started discovering some of its weirder things, and before quantum mechanics and particle physics even existed.

Why do galaxy rotation curves flatten out at large distances? There’s an invisible substance out there that doesn’t interact with anything else except through gravity.

Why does the double slit experiment show that light acts like a wave even when only one particle at a time is emitted? Because light is both a particle and wave.

And don’t even get me started on decoherence, a theory which is absolutely necessary in order to explain some edge cases of quantum mechanics (including keeping it from allowing communication faster than the speed of light), but which has the uncomfortable side effect of creating an infinite number of parallel universes.

Sorry, got off on a tangent there. It’s generally a good saying, it’s just that reality doesn’t always care when humans come up with a good saying.