  Quasiparticle properties are explored in an effective theory of the $t-J$
model which includes two important components: spin-charge separation and
unrenormalizable phase shift. We show that the phase shift effect indeed causes
the system to be a non-Fermi liquid as conjectured by Anderson on a general
ground. But this phase shift also drastically changes a conventional perception
of quasiparticles in a spin-charge separation state: an injected hole will
remain {\em stable} due to the confinement of spinon and holon by the phase
shift field despite the background is a spinon-holon sea. True {\em
deconfinement} only happens in the {\em zero-doping} limit where a bare hole
will lose its integrity and decay into holon and spinon elementary excitations.
The Fermi surface structure is completely different in these two cases, from a
large band-structure-like one to four Fermi points in one-hole case, and we
argue that the so-called underdoped regime actually corresponds to a situation
in between, where the ``gap-like'' effect is amplified further by a microscopic
phase separation at low temperature. Unique properties of the single-electron
propagator in both normal and superconducting states are studied by using the
equation of motion method. We also comment on some of influential ideas
proposed in literature related to the Mott-Hubbard insulator and offer a
unified view based on the present consistent theory.
