  We apply the discrete S_3 flavor symmetry to both lepton and quark sectors of
the standard model extended by introducing one Higgs triplet and realizing the
type-II seesaw mechanism for finite neutrino masses. The resultant mass
matrices of charged leptons (M_l), neutrinos (M_nu), up-type quarks (M_u) and
down-type quarks (M_d) have a universal form consisting of two terms: one is
proportional to the identity matrix I and the other is proportional to the
democracy matrix D. We argue that the textures of M_l, M_u and M_d are
dominated by the D term, while that of M_nu is dominated by the I term. This
hypothesis implies a near mass degeneracy of three neutrinos and can naturally
explain why the mass matrices of charged fermions are strongly hierarchical,
why the quark mixing matrix is close to I and why the lepton mixing matrix
contains two large angles. We discuss a rather simple perturbation ansatz to
break the S_3 symmetry and obtain more realistic mass spectra of leptons and
quarks as well as their flavor mixing patterns. We stress that the I term,
which used to be ignored from M_l, M_u and M_d, is actually important because
it can significantly modify the smallest lepton flavor mixing angle theta_13 or
three quark flavor mixing angles.
