  Since their inception at {\it Macy conferences} in later 1940s complex
systems remain the most controversial topic of inter-disciplinary sciences. The
term `complex system' is the most vague and liberally used scientific term.
Using elementary cellular automata (ECA), and exploiting the CA classification,
we demonstrate elusiveness of `complexity' by shifting space-time dynamics of
the automata from simple to complex by enriching cells with {\it memory}. This
way, we can transform any ECA class to another ECA class --- without changing
skeleton of cell-state transition function --- and vice versa by just selecting
a right kind of memory. A systematic analysis display that memory helps
`discover' hidden information and behaviour on trivial --- uniform, periodic,
and non-trivial --- chaotic, complex --- dynamical systems.
