  Charge symmetry breaking in the strong interaction occurs because of the
difference between the masses of the up and down quarks. At present the
Standard Model can't explain the observed mass pattern (M(n), M(p), m(u), m(d)
etc.) and their hierarchy. The last one doesn't permit us to find the origin of
the isotope effect. The origin of the mass of matter will be clarified when the
mechanism of chiral symmetry breaking in QCD is established.
