At low levels, it's possible to enter scaleable businesses with relatively low risk.
I started writing e-books for an affiliate. Took ~2 weeks to make the first couple books. Early sales justified continuing. Then mid-run sales justified continuing on a longer term scale.
I ran out of books to write, so I didn't scale that high - but I produced some recurring revenue with very little risk. At each point I knew my efforts would pay off at a certain level.
Startups aim to be scalable. But you should note that you don't have to start out scalable. Doing so might be seen as a premature optimization. You could hand-service your first dozen customers, and worry about scaling only when you start counting your customers in hundreds rather than tens.
[0] http://casnocha.com/2009/03/scalable-vs-non-scalable-careers...