  In paper [1] unpredictable points were introduced based on Poisson stability,
and this gives rise to the existence of chaos in the quasi-minimal set. This
time, an unpredictable function is determined as an unpredictable point in the
Bebutov dynamical system. The existence of an unpredictable solution and
consequently chaos of a quasi-linear system of ordinary differential equations
are verified. This is the first time that the description of chaos is initiated
from a single function, but not on a collection of them. The results can be
easily extended to different types of differential equations. An application of
the main theorem for Duffing equations is provided.
