In between his personal exploits baking cookies and coming up with
new regular expressions with his SO in the shower, he explained his PhD
defense, in which one of his committee members asked just that questions--
and when he was done, asked "why is that", and repeated. He had to go, as
this explanation did, from chemical compositions of atmospheres, albedo,
to solar spectra, dipole effects and the photochemical effect.
But basically he was getting into the hierarchical complexity Science uses
at each level.