  A way is suggested to understand why the average masses of $(d,s,b)$ quarks
are smaller than those of $(u,c,t)$ quarks. In contrast to previously proposed
mechanisms relying on different Higgs boson vacuum expectation values or
different Yukawa couplings, the mass difference is explained as a consequence
of mixing of $(d,s,b)$ with exotic quarks implied by the electroweak-strong
unification group E$_{\rm 6}$.
