Laser pulse-induced photodissociation of molecules in rare-gas solids is investigated by representative quantum wavepackets or classical trajectories which are directed towards, or away from, cage exits, yielding dominant photodissociation into different neighbouring cages. The directionality is determined by a sequence of reflections inside the relief provided by the slopes of the potential energy surface of the excited system, which in turn depend on the initial preparation of the matrix isolated system, e.g, by laser pulses with different frequencies or by vibrational pre-excitation of the cage atoms. This reflection principle is demonstrated for a simple, two-dimensional model of F-2 in Ar.