Less than zero
The long tail is real, but sometimes the longest parts reach underwater. When there's enough choices, it means that some things will never get picked.
Charles Blow reports in the NY Times that:
"A study last year conducted by members of PRS for Music, a nonprofit royalty collection agency, found that of the 13 million songs for sale online last year, 10 million never got a single buyer and 80 percent of all revenue came from about 52,000 songs. That’s less than one percent of the songs."
The internet has allowed ease of entry into the market. You can advertise anything, any service, any good, any piece of junk in your garage--essentially for zero. You can go into business effortlessly, telling yourself you'll just hang out on the long tail and do just fine. Understand that zero is a very real probability, perhaps even a likelihood. Derek reminds us that 0% of a really big number is still zero.
What direct marketers have always understood is that you must make something work in the small before you bet the farm and market it to the masses. If you can't sell to 1 in 1000, why market to a million?