I consider a specially designed simple mechanical problem where a “particle acceleration” due to an external force creates sound waves. Theoretical description of this phenomenon should provide the total energy conservation. To introduce small “radiative losses” into the phenomenological “mechanical” equation, I advance first an “interaction Lagrangian” similar to that of the Classical Electrodynamics (kind of a self-action ansatz). New, “better-coupled” “mechanical” and “wave” equations manifest unexpectedly wrong dynamics due to changes of their coefficients (masses, coupling constant); thus this ansatz fails. I show how we make a mathematical error with advancing a self-interaction Lagrangian. I show, however, that renormalization of the fundamental constants in the wrong equations works: the original “inertial” properties of solutions are restored. The exactly renormalized equations contain only physical fundamental constants, describe well the experimental data, and reveal a deeper physics – that of permanently coupled constituents. The perturbation theory is then just a routine calculation only giving small corrections. I demonstrate that renormalization is just illegitimately discarding harmful corrections fortunately compensating this error, that the exactly renormalized equations may sometimes accidentally coincide with the correct equations, and that the right theoretical formulation of permanently coupled constituents can be fulfilled directly, if realized.

equation coupling, renormalization, reformulation, coupled constituents, quasiparticles