Spam works because it scales.
It costs very little to ramp up from 100,000 addresses to 10,000,000 addresses, and all it takes is a couple of hits to make the effort profitable.
How do I know this? Because it exists.
Here’s another example of the principle at play:
On my recent trip to Las Vegas, my wife and I took a couple of walks down the Miracle Mile. We encountered something we did not see in the tourist information: hundreds of day laborers lining the sidewalks, handing out stiff glossy cards.
The cards had pictures of various professional women, with their various phone numbers. The laborers wore t-shirts bearing the names of the various escort agencies they represented. Some even wore backpack harnesses with lighted signs.
As you walk down the street, they will desperately try to hand you a card. Even if you are walking with your wife, holding her hand on one side and with your other hand intentionally in your pocket. The sidewalk ends up making a crunchy noise as you walk on the thousands of discarded ads.
Rarely do you see someone keep the card. It makes you wonder just how effective the strategy really is.
The night we walked, there must have been 300 workers wearing shirts and trying to sell me and my wife a night we’d never forget. Why 300? Why not 200? Why not 400 or 500?
That is the mystery of the Invisible Hand. Over time, there will be feedback to those hiring the workers for nightly work. 600 might be too many, 100 too few. Over the days and weeks, the formula gets refined, where dollars spent on card-hustlers yields trackable and visible results. It may well be that on Wednesdays, 400 are needed to make it worthwhile, where on Fridays and Saturdays there is less need to boost business.
Or, it might be that enough escort agencies are in the game that it’s market share they are after, not trying to grow the overall market.
Or… just maybe, the spammers are just bad at math. Like the one who sent me an email with this subject line:
Female Orgasm – How to Make a Woman Orgasm in 66 Simple Steps
There’s nothing ‘simple’ about 66. (Or maybe they just know 62 things I don’t…)

That is an interesting way to put it. I like it. I get asked all the time why people send spam. This is a good way to explain it. You can also read (self Plug) http://www.zerosource.org/2008/08/why-do-people-send-spam.html
on my math for spam.
what are the four steps you know?
I bet the 66 guy sells some just based on “66? What the heck are all those steps?”