Parallel breakthroughs in the understanding of phase transitions in condensed matter physics led to novel insights based on the renormalization group. They involved the work of Leo Kadanoff (1966) and Kenneth Geddes Wilson – Michael Fisher (1972) —extending the work of Ernst Stueckelberg – André Petermann (1953) and Murray Gell-Mann – Francis Low (1954) —which led to the seminal reformulation of quantum field theory by Kenneth Geddes Wilson in 1975. This reformulation provided insights into the evolution of effective field theories with scale, which classified all field theories, renormalizable or not. The remarkable conclusion is that, in general, most observables are "irrelevant", i.e., the macroscopic physics is dominated by only a few observables in most systems.