In ordinary statistical mechanics, the extensive parameters (such as total energy and volume) are more fundamental than the intensive parameters (such as temperature and pressure) in the sense that the latter are determined a posteriori by the former in the large volume limit. Furthermore, in a finite region of the space of extensive parameters, the corresponding intensive parameters are automatically tuned to first-order phase transition point.
We consider anoalogous situation in quantum field theory. The coupling constants in conventional path integrals are analogous to the intensive parameters in the canonical ensemble. Therefore, it is natural to expect that in general low-energy effective theories, the coupling constants are dynamically fixed a posteriori from extensive parameters in the
large-volume limit, We argue that an automatic fine-tuning is realized such that the coupling constants are fixed at the quantum phase transition point at zero temperature. This occurs even if the transition is of higher order due to the Lorentzian nature of the path integral. This can be the basis for solving the naturalness problem in the fundamental theory such as the matrix models.