I've noticed that the example of a particle in a box is heavily used even for physical situations where there is no obvious box: for example when finding the degeneracy pressure in a neutron star one calculates the fermi-energy from a 3D-particle in a box. So I wondered: is there any good reason why the particle in a box-model holds for a large variety of situations? Does this has to do with the pauli-exclusion principle? I.e. that the position is constrained by ##\delta x \delta_p = \hbar /2## and we can think of these boxes as ##\delta x## wide?