A few weeks ago, I got a check in the mail for $404.79. Before I explain why, I have to digress with a brief story about my dad.

Born in Germany, my dad emigrated to the United States during World War II. Before leaving his homeland at the age of nineteen, he published his first book, a translation of a classic eighteenth-century text on music composition that was revered by Bach, Haydn, Mozart, Beethoven and scores of illustrious others. The original text was in Latin, which my dad translated into German.

Upon arriving here, he was soon drafted into the American army and shipped overseas, ending up back in Europe as a counterintelligence agent tasked with debriefing citizens. The war’s close found him in a town near the famous mountaintop residence of Richard Strauss, legendary composer of Also Sprach Zarathustra (that dramatic music that plays when the apes discover the big thingamajig in the opening of Stanley Kubrick’s “2001”).

So my dad goes up the mountain to interrogate Strauss—and finds the old man teaching his own grandnephew composition out of … (wait for it) … my dad’s book.

After returning to the States, my dad eventually produced another rendering of the book, this time in English, which was published here by W.W. Norton as The Study of Counterpoint. He taught me composition from it when I was a teenager. It is still used in schools today.

And by now I’ll bet you’ve guessed how this all ties in. That $404.79 check was from W.W. Norton: my portion of this royalty period’s proceeds from a book my dad started working on when he was a teenager in the 1930s.

After depositing that check, I went out with my son Chris and bought an LCD monitor he’s been wanting. I doubt that my dad ever imagined, when he was nineteen, that his efforts would someday buy a computer monitor for his twenty-year-old grandson. But that’s exactly what they did.

Residual income is like that; so is love. They both defy the entropy of time. They last.

Of course, most of us will never write a classic textbook on music composition (let alone Also Sprach Zarathustra). That’s where network marketing comes in. To borrow Apple Computer’s old slogan, network marketing is royalties for the rest of us.

A few days later, a much larger check arrived, one that has put a roof over Chris’s head for the past twenty years: the commission check I’ve received every month since joining a network marketing company in the summer of 1986—two years before Chris was born.

Residual income. The best investment ever invented.

JOHN DAVID MANN is Consulting Editor to Networking Times.