LET’S say you wanted to build an advertising-supported online media business that took in $50 million a year in revenue. How many users would you have to attract to get there?

Probably too many for most people to even try, if the numbers run by Jeremy Liew, a venture capitalist at Lightspeed Venture Partners, are accurate. On his blog (lsvp.wordpress.com), Mr. Liew determined that even the type of site that can get the largest advertiser payments per user would have to be immensely popular before it made that kind of money.

The analysis is “sobering,” wrote Tim O’Reilly, the chief executive of O’Reilly Media, a publisher of computer books. “This may be why more entrepreneurs are going for low-investment sites that don’t need an exit but provide ‘lifestyle businesses’ for their owners,” he wrote on Radar, his company’s blog (radar.oreilly.com).

That is, rather than seek venture financing and hire a staff, it may be better for one or two people to create a relatively simple site — say, a hobbyist blog for guitar enthusiasts — and use a service like Google AdWords to, hopefully, make enough money to live on.