  When Anderson localization takes place in a quenched disordered system, a
continuous symmetry can be broken spontaneously without accompanying Goldstone
bosons. Elaborating on this observation we propose a unified, microscopic
physical picture of the phase diagram of both quenched and unquenched QCD with
two flavors of Wilson fermions. The phase with Goldstone bosons -- by
definition the Aoki phase -- is always identified as the region where the
mobility edge of the (hermitian) Wilson operator is zero. We then discuss the
implications for domain-wall and overlap fermions. We conclude that both
formulations are valid only well outside the Aoki phase of the associated
Wilson-operator kernel, because this is where locality and chirality can be
both maintained.
