  It is pointed out that if a flavor symmetry (a discrete symmetry, a U(1)
symmetry, and so on) exists, we cannot obtain the observed CKM quark mixing
matrix V_q and MNS lepton mixing matrix U_\ell, even if we can obtain
reasonable mass spectra under the symmetry. Such the serious constraint is
derived only from the SU(2)_L conditions, and we will not assume any explicit
flavor symmetry and/or any explicit mass matrix forms. And then, we will
discuss the meaning of the severe constraint.
