  If primordial fluctuation is Gaussian distributed, higher-order cumulants of
the cosmic fields reflect nonlinear mode coupling and provide useful
information of gravitational instability picture of structure formation. We
show that their expected deviation (sample variance) from the universal values
is nonvanishing even in linear theory in the case where observed volume is
finite. As a result, we find that the relative sample variance of the skewness
of the smoothed velocity divergence field remains as large as $\sim 30%$ even
if the survey depth is as deep as $\sim 150h^{1}Mpc$.
