"In the case of the strong interactions, there was a wealth of experimental data, much of it of high precision. Hadronic masses and magnetic moments, nuclear binding energies and transition rates, many things were measured with great accuracy. But the strongly interacting world was so complicated that most of the experimental data was hard to interpret. Only a fraction of the experimental knowledge of strong interactions, such as the scaling behaviour in deep inelastic electron-nucleon scattering, gave simple clues about the underlying quark-gluon world. As a result, experimental clues alone did not suffice."