  Gravitational falling in AdS has two characteristic properties \cite{ohsin}:
i) A thick shell becomes a thin shell. ii) Any shape become spherical. Such
focusing character of AdS, for the collapse of dusts, leads to the rapid
thermalization mechanism in strongly interacting system. For the collapse of a
wave, it explains the cascade of energy to UV through repeated bounces, which
has been extensively discussed in recent numerical works. Therefore the
focusing is the physical mechanism of instability of AdS. Such sharp contrast
between the dust and wave in collapse, together with the experimental
observation of rapid thermalization, suggest that the initial condition of
created particles in RHIC is in a state with random character rather than a
coherent one. Two time scales, one for thermalization and the other for
hydro-nization are defined and calculated in terms of the total mass density
and energy distribution of the initial particles. We find $t_{th}\sim
(1-c_1/E^2)^{1/2}/T $ so that softer modes thermalize earlier. However, for
hydro-nization, $t_{hyd} \sim 1/E^{2/3}T^{1/3}$ therefore harder modes come
earlier. We also show that near horizon limit of Dp brane solutions have
similar focusing effect which is enough to guarantee the early thermalization.
