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!


K. Boulding