At a base level, we have some fundamental degrees of freedom and interactions between them. On some level, if we knew what those degrees of freedom were and what equations described them, all of physics would boil down to to solving the fundamental equations for those interacting degrees of freedom.
However, (a) in particle physics we don't know what those fundamental degrees of freedom are, and (b) even in condensed matter where we usually know the degrees of freedom are electrons, photons, and nuclei, the equations are much to difficult to solve exactly. Furthermore, it is usually the case that when we make observations, we don't directly probe the fundamental degrees of freedom, but some larger scale collection of them. Then it turns out that we can organize the physical effects the theory produces, by how important they are to a coarse grained observer.
The Wilsonian renormalization group is a systematic way of describing how to organize the effects of coarse graining some fundamental interactions over some length scale. The underlying collection of interactions and particles produce emergent phenomena that depend on the length scale at which we look at those phenomena. The magical simplicity of effective field theory is that we can often capture that scale dependence in the 'running' of some constants of low-dimension operators in an effective action. Provided we are at "large enough distances" (compared to some underlying physical scale), the detailed effects of the fundamental interactions tend to wash out, and we are left with a simple effective description that is determined by the symmetries of the system and the effective interactions that dominate at low energies.
