There is no such thing as a free variable.
Every program has (at least) two purposes: the one for which it was written and another for which it wasn't.
In software systems it is often the early bird that makes the worm.
If a listener nods his head when you're explaining your program, wake him up.
The best book on programming for the layman is Alice in Wonderland, but that's because it's the best book on anything for the layman.
FORTRAN is not a flower but a weed - it is hardy, occasionally blooms, and grows in every computer.