Strong interaction

"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."

"The strong force may not unify with the other forces. There’s no evidence for unification in our Universe so far, as proton decay experiments have come up empty. The initial motivation is flimsy here as well: If you put any three curves on a log-log scale and zoom out far enough, they will always look like a triangle where the three lines just barely miss coming together at a single point."