A system is a big black box Of which we can’t unlock the locks, And all we can find out about Is what goes in and what comes out. Perceiving input-output pairs, Related by parameters, Permits us, sometimes, to relate An input, output and a state. If this relation’s good and stable Then to predict we may be able, But if this fails us—heaven forbid! We’ll be compelled to force the lid! —Kenneth Boulding,2 economist
