  We discuss why the SU(3)^3 supersymmetric model with the most general
superpotential can naturally break to the standard model if gauge singlets and
a discrete symmetry are included. This mechanism does away with the need for
fine-tuning in the form of the assumed absence of certain terms in the
superpotential. It also automatically guarantees that any abelian discrete
phase symmetry of the GUT will survive the symmetry breaking. Such a discrete
symmetry, also known as the matter parity, is needed to suppress both proton
decay and the flavor changing neutral current (FCNC), and may help solve the
hierarchy problem.
