Julian Schwinger Quote

Is the purpose of theoretical physics to be no more than a cataloging of all the things that can happen when particles interact with each other and separate? Or is it to be an understanding at a deeper level in which there are things that are not directly observable (as the underlying quantized fields are) but in terms of which we shall have a more fundamental understanding?

Quantum Mechanics - Symbolism of Atomic Measurements (2001) p. 24 f.