This is really a quote attributed to
Einstein in reference to the randomness inherent in
quantum mechanics. Einstein believed that quantum
theory could not be true, simply because it implied there was a limit to how much a scientist could know about a
particle. Everything else, therefore, appeared random to an observer (see
Uncertainty Principle,
Schrodinger's Cat.)
Einstein struggled through the last half of his life to eliminate this
uncertainty, but he never could (no one else could eliminate it either, and since Einstein we have only realized more things that we can't know. see
neutrino). Some say (read:
Hawking, who is very hung up on comparing himself to Einstein,
btw) that never conceding this fact was Einstein's greatest mistake.
All of this is quite ironic considering Einstein never believed in a science that he helped to found.