I've not seen it before, and thought you'd enjoy it.
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.
...there's more, of course. But I'm not convinced that posting the whole thing is a fair (ab)use of copyright. You'll find it on less fussy people's sites. Go fish.
* That's an Amazon affiliate link... trying it out.